Common Engine Noises: A Comprehensive Guide with Diagnosis, Symptoms and Fixes


 If there is one thing car owners hate to hear, it is noises coming out of the engine. Yes, cars can make a whole lot of strange sounds, from clunking, knocking, rumbling to humming and hissing.

In the engine’s defense, there is a whole lot ofmoving parts in motion every time you turn it on.  It is actually a surprise it’s not louder.

Even then, engine noises are more often than not an indication of a problem in the system, some serious and some not. Here is a list of some common engine noises which you are likely to experience with a brief explanation of what causes them.

What causes engine noises?

 Engine Knocking Sounds

Knocking sounds coming out of the engine, also called pinging can be disturbing and worrying. They are caused by uneven burning of fuel in the cylinders. Ordinarily, there is an intricate balance of air and fuel. The fuel burns in small, regulated pockets and not haphazardly or all at once.

When each pocket burns, a small explosion is crated which ignites the burning of the next pocket and so on. When you hear knocking sounds it means fuel is not being burned in measured pockets and the little explosions are happening haphazardly.

Apart from the annoying sounds produced, this could cause damage to engine cylinder walls and pistons.

Possible causes:

  • Low Octane Fuel

Octane ratings in fuel refer to its ability to resist premature detonation. Every engine is designed to work with fuel of a certain octane rating. If you fill up you tank with fuel whose rating is lower than what your engine is designed for, knocking sounds will be heard as you drive.

To make sure this doesn’t happen, always use gas which is at or above the octane rating recommended by the vehicle manufacturer. If you accidentally fill up with something lower, use an octane booster which you can buy at any auto parts store. It works by raising octane levels and helps stop the knocking.

You can get octane boosters for a range of prices, between $30 and $100. The Less expensive ones offer basic functionality and the pricier ones are made from high quality ingredients for superior performance.

  • Carbon deposits

Gasoline and diesel are made up of carbon molecules. When they combine with oxygen and burn, residual carbon is formed. It sometimes forms deposits on spark plugs and other components of the combustion system. Increased carbon deposits in the cylinder reduces their volume and increases compression.

This problem can be dealt with by using a fuel injector cleaner designed to clean out deposits. This cleaner costs between $50 and $80 and takes a couple of hours to work its magic.

Rattling Noises

Rattling on cold starts

Rattling or clicking sounds on cold start are unquestionably audible when you first start the engine especially on a cold morning when the car has had more than a few hours or rest. After a few minutes of engine running, the noise usually goes away on its own.

This is most likely caused by a condition called ‘piston slap.’ To confirm if it is the problem, use a mechanic’s stethoscope to identify exactly where the sound is coming from. If it’s coming from the valve cover, it’s likely to be a valve train issue. If it’s from the side of the engine block it is probably a piston slap.

Piston slap:Ordinarily a piston fits tightly into a cylinder and moves up and down in a snug space. If there is some wiggle room, the piston rattles against the cylinder wall. To repair this, you need an engine rebuild which could cost up to $4,000.

Rattling on acceleration

If the rattling sound is heard when you accelerate, it points towards a problem with the timing belt. Timing belts are kept tightly in place using a tensioner. If this tensioner loses strength the belt gets lose and starts to move more than it should. It is this extra movement which causes rattling when accelerating.

It will cost you between $500 and $1,500 to replace a timing belt and/or tensioner. Left unattended, the problem could cause the belt to break which could then cause engine failure.

Clicking Sound As Engine Is Running

Clicking sounds from the engine when it is running are most likely to be caused by insufficient amounts of oil. The main function of oil in your engine is to lubricate moving parts. Although you may not notice much difference as oil levels fall, when they approach dangerously low levels, you may hear some clicking as parts knock or grind against each other.

How much oil do you need?

Most engines require between 5 and 8 quarts of oil depending on engine size. 4-cylinder engines for instance require about 5 quarts of oil and 6-cylnder engines need about 6 quarts or oil. Use the markings on the dipstick as a guide so as not to put too much oil.

If nothing is done, the engine bearings could eventually fail and cause permanent engine damage. Be sure to check your car’s oil levels regularly so it never runs out.

Repair costs.

These are dependent on the extent of damage caused by lack of lubrication. You may need to replace pistons, the timing belt, camshaft bearings or connecting rods. If you need all of these, you are probably better off replacing the entire engine assembly. For an average car this would cost you between $3,000 and $4,000. If yours is a luxury European car, engine replacement will cost you about twice as much.

Apart from oil levels, it is also important to make sure your oil is clean. Dirty oil in an engine could be just as harmful as no oil. When it becomes thin and is full of dirt and debris it becomes corrosive. This then speeds up wear of engine parts.

Squealing Sound As You Accelerate

High pitched squealing noises heard when you accelerate is likely to be caused by a loose or worn out fan belt. This is a flexible rubber belt which holds certain engine components together, that is the alternator, crankshaft pulley and cooling fan.

After 60,000 to 100,000 miles (average lifespan of a fan belt) it starts to get worn out. This makes it stretch. When you press the accelerator pedal and gradually increase speed, the pulleys in the engine turn faster than the belt can keep up with. This is what causes squealing on acceleration.

How to identify a worn out fan belt: Like many other aspects of life, prevention is better, and cheaper than cure. A healthy belt has grooved sides or one smooth surface. As long as these sides are free of cracks, your belt is in good condition. Cracks are a sign of old age. The belt will eventually break, leaving you stranded on the side of the road.

Also ensure that your fan belt doesn’t have frays at its edges. A frayed belt is a sign that it is tracking wrongly across the pulleys and can snap any time.

Cost of replacement: It will cost you between $100 and $200 to have your fan belt replaced. The belt itself costs between $25 and $75 and labor will cost between $80 and $120. Labor costs for the job are dependent on how easily accessible the belt is. Some car models’ fan belts are easily accessible meaning it will take the technician less time to remove and install a new one. In other models, the process is quite complex and could take several hours to remove and install. The more time spent on the job, the more you have to pay the technician.

Grinding Noise as You Shift Gears

Shifting gears even in a manual vehicle should be smooth. There should be no jerking and definitely no grinding feeling or noises.

More often than not, grinding of gears happens as a result of driver error. It takes a fair degree of precision to push the clutch pedal down, shift gears and then release it… all smoothly. If you press down too early or release a second or two late, the smooth transition is lost. Plus some vehicles are more sensitive than others.

In other instances, gears grind even when the driver does everything correctly and this could be as a result of a transmission, gear or clutch problems. Sometimes there may be a small piece of metal or some other contaminant in the gear box causing the problem.

It could also be that transmission fluid is running low or burnt meaning that parts are not being sufficiently lubricated. Another possibility is that the transmission filter or pan gasket need replacement. Don’t forget that the transmission is not designed to last the life of a car so it could also be nearing the end of its lifespan.

What to do.If you  are sure that grinding noises when shifting gears are not as a result of driver error, the best way to find out exactly what the problem is and have it fixed is to take your car for transmission service. It is not required as often as regular car service but is still necessary. Most manufacturers advice it every 30,000 to 60,000 miles. Intervals may vary depending on the specific type and age of the vehicle.

What will it cost you? The cost for transmission service varies depending on the kind of repairs and replacements required. You would be looking at an average cost of between $200 and $500 for basic work. If more complex work is required and a complete transmission replacement is necessary, you would be looking at anything between $1,000 and $5,000.

To avoid such hefty bills, don’t skipscheduled services. This way your mechanic can catch issues with the transmission early and avoid major replacement work later.

Crankshaft Bearing Noise

The crankshaft is part of your car’s engine which serves to convert linear motion energy of the piston into rotational motion which is then delivered to the gearbox and wheels. It is the connecting link between the engine and gearbox or drive shaft.

Crankshaft bearings support the crankshaft and also serve to reduce friction between a rotating crankshaft and a stationary engine block. Noises from these bearings are generally caused by low oil pressure which usually damages the surfaces of the bearings. If nothing is done, damage is likely to extend to the the crankshaft. The rumbling or thumping sound from deep inside the engine would usually be heard when accelerating.

If you hear this noise, it is extremely important that you stop running the engine to minimize extent of damage. A mechanic will first remove the oil pan and inspect the bearings to determine how much damage has been done. If it is not extensive, you will probably only need to replace the bearings and solve the oil pressure issue. There are several possible reasons behind low oil pressure which all have to be explored.

Costs: A crankshaft repair costs between $50 and $105 plus labor costs ranging between $130 and $165. If you continued running the car after hearing the noise, damage may have extended to the crankshaft which will then need to be replaced. A new crankshaft costs between $150 and $250.

Whining Noise

Whining noises can be caused by one of several problems in the engine. The first step in identifying the problem is to take note of when the whining sound is heard or when it is loudest. Sometimes there is no whine until you turn the wheel to take a corner. Other times it is loudest when you accelerate and other times it is only there when idling.

Whining when turning:If your car seems to be protesting when you turn, then there is probably a problem in the power steering system. It could be that your steering belt is loose or damaged. If it is loose it only requires some tightening. If it is damaged, it has to be replaced. Replacing a steering belt will cost you between $90 and $200. The belt itself costs $25-$75 and labor costs account for the rest.

Another reason you may hear whining while taking turns is if power steering fluid levels are low or it is dirty. A standard power steering fluid flush, which is what would be recommended, costs between $99 and $125.

A less likely problem, but still worth checking, could be a leak in the power steering liquid pump.

Whining when accelerating:  If all is quiet until you start to accelerate, whining could be caused by a transmission problem. The most likely issue is worn out gears. Gear replacement cost depends on extent of damage. If you have to replace the entire system, it will set you back at least $4000.

Whining when idling: If this is the case, you are probably low on oil. It could be that you haven’t topped up in a while or there is an oil leak.

 Clunking Noise

Clunking noises at the rear on rough road: Clunks on the rear, bottom of the car are most likely caused by a worn ball socket in a sway bar link. Just looking at the outer hub on each side will not reveal much.

The best way to deal with it is to replace both link assemblies. It is advisable to replace both even if only one is faulty.  When one gets worn, the other is likely to do the same soon. Replacement doesn’t cost much and can be done quite quickly when the car is jacked up in the air and tires off.

Clunking when you accelerate:If the annoying clunking sounds cannot be heard until you place your foot on the accelerator pedal, there is probably a problem with the engine mount. An engine mount is the part which holds the engine. In most cars, the engine and transmission are bolted together to make sure they stay in place using 3 or 4 mounts. Some cars have mounts filled with liquid in order to dampen vibration.

When the rubber in these mounts wears out, the engine is no longer held firmly so it may move more than it is supposed to. The result is hard clunking especially on acceleration. Even if only one mount is worn out, it is advisable to replace them all at once. If one is worn out, chances are that the others are not far behind.

Engine mount replacement will cost you between $ 220 and $570 for both the parts and labor. You can opt to buy the mounts online for between $40 and $150.

Ticking When Car Is Idle

Ticking could be caused by one of these issues:

Low oil level: When oil levels in the engine are low, ticking is heard because valve train components are not well lubricated. This can cause significant engine damage so it is the first thing you should check as soon as you hear ticking coming from the engine. If oil levels are low, top it up immediately. If it is old and dirty, flush it out and put in clean fresh oil.

Don’t forget that different vehicles require different types of motor oil. Check the owner’s manual to find out what should and shouldn’t go into your engine.

Rod knock. Ticking can also be caused by rod knocks. It could be caused by a bad bearing in a connecting rod. As it wears out, the bearing gradually allows movement and the playing causes tapping or clunking.

Worth noting is that this issue causes tapping which increases as RPMs increase and slows down as they reduce. When a rod knock is the problem, tapping will not change with engine load or engine temperature.

Bottom Line

Finding the source of an engine problem requires some attention. You need to pay enough attention to determine details such as when the noise is heard. Does it come when the car is idling, when accelerating or when braking? The other detail to look for is a general direction from which the noises are coming. Is it under the hood, is it more towards the left, right or the rear? All these will lead you closer to a solution.

Whether it is a rumbling, clunking or knocking sound, the bottom line remains the same. It is your engine trying to speak to you, to tell you it needs your attention.

This is why drivers are advised against ignoring them. Always take your car to a repair shop as soon as you start hearing an abnormal noise. Even if you have to spend some money for repair or replacement of parts, it will cost you less than it would have cost you if you waited for it to get worse.


What causes a humming sound when idle?

Humming engine sounds at idle could be caused by problems with the drive belt or parts which are driven by the drive belt like the power steering pump, water pump or air conditioning compressor. An air leak could also cause humming. This could be a leak in the air conditioning compressor, water pump or power steering pump.

How do I listen to engine knock?

A mechanic’s stethoscope is an extremely useful tool when it comes to diagnosing mechanical problems. When you are dealing with a system as complicated and ordinarily noisy as an engine bay, it can be difficult to figure out exactly where a certain noise is coming from.

Considering identifying the source of a noise is the first step towards solving a problem, it is imperative that a mechanic correctly identifies the source.

It is also useful given that as cars get older, it is common for them to develop multiple problems at a time. Without a stethoscope, it can all sound like a big bad band of clinking, knocking and hissing everywhere.

Can I continue driving with engine noises?

It is recommended that you take your car to a professional mechanic as soon as you start hearing engine noises. Yes, there is a chance that the technician will send you home with a clean bill of health and tell you that there is nothing to worry about, but that is unlikely.

Some instances, such as loud, hard knocking in the engine call for an immediate stop. It may not even be safe to keep driving to the nearest auto repair shop.


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