15 causes of humming noise in the car

Humming noise in the car can be heard especially when driving and it can occur for various reasons. It is important to know exactly where the humming sound comes from because this can indicate a serious problem with the car that needs proper repairs.

Some cars, like Mercedes-Benz, have a component called a hydraulic pulsation damper. They work in active suspension systems, as well as other systems that use a hydraulic drive. If they fail, hum and vibration may be heard in the operation of such systems, and they will need to be completely changed.

Possible reasons for hum noise in the car

A bad wheel bearing

This is the most common cause of why you will hear humming noise in the car when driving. You can easily know you have a failing wheel bearing because as you increase the speed the hum becomes much higher in intensity and under a variety of conditions: on a straight road, when turning when driving on roads with different surfaces.

Check out additional info on a bad or failing wheel bearing

Another simple method of checking if you have a bad wheel bearing is by jacking up the car. It is necessary to set the speed to neutral so that the wheel rotates freely (this can be omitted if wheels are being checked on a rear-wheel-drive car. When you see that the wheel rotates with ease, you should rotate it by hand as quickly as possible to hear the hummin noise.

It is more difficult to diagnose the condition of the wheel bearing for four-wheel-drive cars. To do this, you need to lift the car. The checking procedure is the same, but in some cases, it is necessary to use a stethoscope.

If you found one or more damaged bearings, then you need to change them as soon as possible. Driving with a bad wheel bearing is very dangerous, especially if it is heavily worn. 

In addition, a damaged bearing is sometimes difficult to remove. Because it is heated in motion, it can stick, and this is caused by driving like this for a longer time.

Power steering pump and its hoses

A damaged power steering pump can also be responsible for a humming noise. Often you can hear the hum when starting the car after when cold because the oil thickens at low temperatures. So, after starting the car you will hear the hum for 2-3 minutes because the pump tries to pump thick liquid.

In this case, you should replace the hydraulic booster fluid with one that would not freeze in low temperatures, and it is also recommended to revise the pump to prevent its breakdown.

The humming noise can also appear in the hoses of the power steering hoses because of their improper placement, and this symptom can be heard when the engine is idle.

You can diagnose the hoses by turning the steering wheel in one direction or another. If the sound changes at the same time, it makes sense to check the correct placement of the hoses, they should not bend.

Often problems with these hoses were observed in Mercedes-Benz cars with the “Active Body Control” feature. You can check it by driving at low speed on uneven roads or swinging the car. In this case, the nature and intensity of the hum will change.

A damaged inner CV joint

An inner CV joint is a part of the transmission and its role is to send torque to the drive wheels. If this piece is damaged, then it is possible to hear a hum under the car. The symptoms are somehow similar to a damaged wheel bearing, the noise increases when the car speeds up.

However, the noise resembles more of a crackle and it can also be heard when you are in a turn. Hum in a CV joint can appear because:

  • Using a bad lubricant or due to lack of lubrication.
  • Significant CV joint wear due to natural causes such as aging, and also caused by aggressive driving style

A worn input shaft bearing

Humming noise can also be caused by a failing input shaft bearing located in the transmission, so the noise will be under the car, the higher the speed, the louder the hum.

Checking this issue is easy, you just have to shift gear to neutral while driving, if the humming noise disappears, then the input shaft bearing is damaged and you should replace it at a car workshop because it’s a hard operation.

A failing alternator

If the alternator is not working properly this could also cause humming noise. A damaged alternator means that the normal voltage will not be maintained in the car’s electrical system. This will cause engine system failures, the electronics in the cabin to not function and the battery to not be charged properly.

A damaged water pump bearing

If the bearing from the water pump is worn out this will trigger a hum in the engine compartment. If it’s partially failed this will mean that the engine temperature, including the coolant temperature, will be above normal, so you will have to be careful and change the bearing or the entire pump as soon as possible.

Low transmission oil level

Low oil level in transmission whether your car has a manual or automatic transmission can cause a humming noise when driving. At a higher speed, the sound will be louder. This is a very serious problem since you cannot use the transmission like this, this will significantly reduce its normal operation.

The recommendation is to check the problem and replace the whole fluid, and not complete the old one.

Worn rear axle reducer

If you have a rear-wheel-drive or all-wheel-drive car then the humming noise can be caused by a worn-out rear axle reducer, especially if the noise is heard from the back of the car. Like in the case of a damaged wheel bearing and low transmission oil level, the sound is louder.

The wear of the rear axle reducer can be caused by a low oil level in the transmission or because the oil is worn, and if the transmission itself has problems.

Worn release bearing

If when you press the gas pedal a humming noise is heard, then, most likely, the release bearing is damaged and needs to be replaced. For this, you should change the entire cluck kit, not just the bearing.

Loose engine screws

The vibration caused by loose screws can resemble a hum. This is easily resolved by tightening the screws

Worn universal joint shaft

If the hum comes from under the car then the possible reason can be a worn universal joint shaft. Checking it requires you to be under the car and some mechanical skills.

Using winter tires in summer

Driving with tires that have rubber made especially for colder seasons on a warm road can emit a humming noise. To get out of this situation, you just need to replace the winter tires with summer tires.

Incorrect wheel balancing

Unbalanced wheels will vibrate when driving. The higher the speed, the higher the vibration. This is not only the cause of discomfort for the driver and passengers but also the cause of the hum. And the more unbalanced the wheels are, the louder the hum will be. Therefore, it is necessary to balance the wheels at a car workshop.

Exhaust pipe

A rare case of humming noise, especially at certain engine RPM can be caused by the fact that the exhaust pipe is not fixed in its place, and will touch other car elements.


If you had the patience to read the entire article, you realized that there are quite a few parts that can cause humming noise. If you experience this issue check the wheel bearing first because this is the most common cause.

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