What causes humming sound in my car

Hum in the car while driving can occur for a variety of reasons — failure of the hub bearing, wheel imbalance, transmission problems and others. It is important to distinguish the origin of these noises, as the reasons why they occur can be critical.

If the hub bearing fails (which is the cause of the car's humming while driving in most cases), it is undesirable to operate the car at all until the problem unit is replaced, because it is simply unsafe both for the driver and passengers, and for other road users.

Noises you can ignore

Depending on the degree of noise isolation of the car, the driver and passengers may always hear some noises. Noises that should not be feared while driving include:

  • A strong headwind or side wind when driving on the highway. This is especially true for driving at high speeds and for cars with a small-sized body. To eliminate the hum in this case, it is necessary to slightly reduce the speed of travel.
  • Engine operation. Any internal combustion engine makes noises during operation. But if the engine suddenly began to work much louder than before, it is necessary to perform additional diagnostics.
  • Driving on a bad road. In particular, driving on coarse-grained asphalt always makes more noise than driving on smooth pavement.

Causes of hum in the car

There may be about 10 causes of noise that need attention.

  1. the hub bearing has failed;
  2. brake pads in a caliper;
  3. wear of the internal CV joint;
  4. power steering pump failure;
  5. worn out bearing in the attachment (in the pump or alternator);
  6. bearing collapses in gearbox (it is actual in gearbox for release plate and primary shaft bearing);
  7. low oil level in the transmission (transmission gearbox, gearbox);
  8. wear of propeller shaft cross (typical problem for 4WD);
  9. wheel imbalance;
  10. defect on the tire.

Therefore, below we will consider what can cause the hum, how serious the cause and how to diagnose it.

What does humming sound like

The hum slightly reminds the idling of a truck engine. Sometimes it can be a distant, humming noise in car. It can start suddenly and disappear just as quickly. When driving on the highway, the hum may gradually increase in intensity. In some cases, the sound may be too loud and unstoppable.

How to determine the cause of hum in the car

The most common cause of hum in the car is the failure of the hub bearing. When the hub malfunctions, a humming noise can occur in motion, when turning, when driving on roads with different surfaces.

Hub or not?

Signs of a failed hub bearing on one of the front wheels may include the following:

Damaged hub bearing

  • The hum level in the car at the front or rear increases as the car accelerates;
  • the roar in the car increases when you turn the wheels to one side or the other, and decreases again when putting the wheels straight (and the more abrupt turn and at higher speed — the higher the probability of failure is the hub bearing and is an indicator of the degree of its wear)
  • At high speed (up to 60 km / h and more) hum in the car becomes «as in an airplane», that is, very much, and with increasing speed this hum increases;
  • At high speeds besides the hum there is also a vibration of the steering wheel (in especially «neglected» cases and the vibration of the whole car, especially it is noticeable when driving on a smooth and flat road).

The reason that the hum in the car when turning increases, is that in this situation, the weight of the car by inertia moves to one of the front hub bearings, that is, the load on them increases (when turning left, the load increases on the right front bearing, and when turning right — on the left one).

To check the hub bearing you need to jack up the car under the wheel whose bearing you want to check. The car must be in neutral speed beforehand, so that the wheel can turn freely. Also beforehand it is necessary to put the car on a handbrake or set the chocks (handbrake is not necessary to be switched on in case a car owner plans to check the rear hub bearings).

Checking the hub bearing

The unscrewed wheel should be turned by hand, trying to give it a high speed, so that the hum, if any, was clearly audible. Also need to jerk the wheel in the vertical plane (at the same point to push away and toward you). If there is a play and the wheel deviates from a strictly vertical position, it means that the hub bearing is out of order.

It is also possible to diagnose the hub bearing failure by vibration (if I obviously don't hear what's buzzing in my car when unscrewing the hub). To do this, you need to unscrew the diagnosed wheel, and hold the hand on the nearest to it element of car suspension. The best way to do this on the front axle is to use the spring plate of the shock-absorbing strut, or the protruding part of the knuckle.

When checking the bearings on the rear axle, use your hand to hold the elements of the shock absorber with spring, the arm nearest to the hub, or the nearest part of the beam. If there is vibration on the above mentioned elements while turning the wheel, it means that the hub bearing is out of order.

It is more difficult to diagnose the condition of the bearing for four-wheel drive cars. For this purpose it is necessary to drive it on an elevator. The checking procedure is similar, but in some cases it is necessary to use a stethoscope (sound amplifier).

On the road, when driving, you need to choose a safe stretch of road (or pad) where you can accelerate and try to enter sharply into turns. If at such bends the hum will amplify — it means the hub bearing is really the problem. As a last resort, you may always ask for help in diagnostics at an auto service.

It's not recommended to drive on a bad wheel bearing more than 1000 miles. Decrease your speed.

Driving with a faulty hub bearing is very dangerous, especially with its significant wear.

Problems with the brake system

Typically, when braking, the pads may squeak or squeak. This sound cannot be confused with a hum. However, if there is a problem with the caliper guides or heavy wear on the brake disc or the pads themselves, the sound can become similar to a hum. You should remove the caliper and check the condition of the guide pins and brake surfaces.

How do I know if a constant velocity joint is humming?

Checking the condition of the CV joint

If it is the inner CV joint that is damaged, there is often a humming sound under the car, as it is part of the transmission system, and transmits torque to the drive wheels. The sound is more like a crunch, and it increases, first, when entering a corner (especially at high speed), and second, at high speed. Because of which it may seem that it is a hum. Reasons for the appearance of hum due to the internal CV joint may be:

  • Lack of lubrication inside.
  • Damage of the dust cover during operation and dirt getting inside.
  • Wear on the internal CVUJ.

How to determine the hum of the power steering pump?

Most often, a hum of the power steering pump occurs during the winter cold season (as a result of thickening of the fluid). A short time after starting the engine (usually two or three minutes) at idle rpm the power steering pump hum is heard.

Checking the power steering pump fluid level

But sometimes the problem is not in fluid, but in kinked hose of its line. In such cases the hum disappears when revs are increased. This problem can be diagnosed by twisting a steering wheel to one side and the other. If the sound changes — it makes sense to check the correctness of hose routing (they must not bend anywhere).

Also owners of Mercedes-Benz vehicles with active suspension system (Active Body Control) have similar problem. In their case, the bending of hoses occurs as a result of a large number of different tubes under the hood. You can diagnose such a breakdown by driving at a low speed on rough roads or by rocking the car on a parking lot. At the same time, the nature and intensity of the hum will change.

How is the pump or alternator bearing diagnosed?

Worn bearings in the attachment will emit a hum from under the hood. If it is the pump that is humming, it will not be working fully and the engine (antifreeze) temperature will rise. If the alternator bearing is worn, the hum will increase over time and the car's electrical system will not maintain normal voltage.

Bearing wear in the gearbox

In case there is a hum under the car, the primary shaft bearing located in the gearbox may be the cause. The higher the speed of the car, the stronger the humming sound will be produced.

This failure is diagnosed in motion. If the sound disappears in neutral, it means the transmission primary shaft bearing is out of order.

Primary shaft bearing replacement

If the hum appears at the moment of depressing the clutch pedal, the release bearing in a gearbox is likely to be out of order. Accordingly, it is necessary to dismantle the clutch, inspect the bearing and if necessary replace it with a new one. Often then the whole clutch set is simply replaced.

In fact, many bearings in a car can be a source of hum. And to understand which one of them makes an unpleasant sound is quite difficult. Let's list those that are predisposed to it:

  • the driveshaft support bearing;
  • the bearing in the transfer case;
  • the bearing in the drive axle;
  • the intermediate bearing on the half axle;
  • gearbox bearings.

Bearings replacement is necessary to be carried out only in automobile service center, independent replacement is hardly possible because of complexity of assembling, disassembling and works connected with gearbox disassembly. In addition, special tools and equipment are often required.

Low transmission oil level

If the transmission oil level is low (whether it's manual or automatic), there's a very good chance that the hum is coming from the transmission. And the higher the speed and/or load on the gearbox, the stronger the noise will be. The hum in the car is usually heard from underneath.

Low oil level in gearbox

It is a serious problem, because you can not use gearbox «dry», such exploitation reduces its life. Check the level of lubricating fluid in the gearbox, and if necessary top up or fully replace it.

When the sound comes from the rear axle of four-wheel drive or rear-wheel drive car, the problem is most likely with the rear transmission. The intensity of hum in this case will increase with the speed of the car (increase the number of shaft revolutions).

There can be two reasons for this:

  • there is little or no lubricant in the gearbox;
  • Partial failure of the reducer itself.

To understand what exactly happened to it is possible when draining transmission oil from it. If it is black, burning, and smells bad — change the oil. If you can see metal suspended particles, shavings, pieces of iron — you need to replace the reducer.

Problems with PTO shaft

If PTO shaft is out of balance due to cross shaft or intermediate bearing wear, you will hear a rumble when driving from the rear of the car. The higher the speed and/or load on the rear axle, the louder the sound will be.

To check it, you need to use an inspection pit or an elevator to provide normal access to the assembly. Next, use one hand to grasp the driveshaft and the other to clamp the drive pinion flange. Then slowly, while holding the clamped flange, try to twist the PTO shaft and flange in different directions. If you can not do it, it means there is no wear, but if you can do it, there is wear.

Wheel imbalance

Unbalanced wheels cause the car to vibrate in motion. The higher is the speed, the greater is the vibration amplitude. It is not only the cause of discomfort for the driver and passengers, but also the hum. And the more unbalanced the wheels are — the more vibration and hum will be. This problem can be eliminated by balancing the wheel at the tire shop.

Note that the noise in the car when driving and braking can also occur when the wheels are overinflated, or when installing rubber that rotates in the opposite direction from the intended (many tires have a special signal arrow indicating the direction of their rotation).

Defects on the tire

Bad tires can also make a humming noise. On the rubber, due to the strong impact of the wheel or manufacturing defect may occur local swelling, in the tread may be clogged with dirt or small stones. All this leads to wheel imbalance, vibrations, uneven tread wear, and body rocking. To see if there are any such defects, you can visually inspect the wheels.

Remember, if there is a noise in the cabin (and moreover, a strong one), it is necessary to perform diagnostics of the abovementioned assemblies. The sooner it is done, the safer driving will be, and expensive repairs can be avoided.


  • Why does my car have a humming noise when I drive?

    There are a lot of causes of something’s humming in my car: the hub bearing, worn internal CV joint, faulty power steering pump, worn out bearing in the attachment or low transmission oil level.

  • Why is my front end humming?

    If you turn the steering wheel to the right or left and the humming noise increases, the problem is in one of the wheel bearings. Sometimes such a noise can be produced by transmission.

  • How do I stop my car from humming?

    Firstly, you should check the condition of the hub bearing. If it functions normally, it's time to replace the CV joint, because it probably can be fully worn out (especially if you hear crunch noise when driving). If not — check oil level in the gearbox.

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