Updated at: 21-07-2022 - By: Lucas

When a car’s transmission fails, whether it is manual or automatic, the noises it makes are one of the first signs that it is deteriorating. Because of worn bearings, shaft gears, and differentials, a manual car makes a hum noise.

It is common to hear a buzzing noise in an automatic transmission due to low oil levels and issues with either the torque converter or the lever arm.

When you hear noises in a manual or automatic transmission, the first thing you should check is the oil level. As soon as you notice a low oil level, you may either add extra oil until it reaches your target level; you can also examine the seals and gaskets if you suspect a leak.

In an automatic transmission, the fluid level is checked more frequently because the oil must be changed after a set number of kilometers (60, 000 km or 70, 000 km) (37. 000 miles 43. 000 miles). You might be able to get away with a short-term fix like a transmission additive. It will lessen the hum and buzzing to some extent, but not eliminate it. In order to do this, you must remove the transmission and thoroughly investigate the issue.

Why does the car transmission make noise?

transmission bearing noise

Low level of transmission fluid

Transmission noise is almost often the result of a leak in the fluid. Car transmission noises are caused by a lack of oil and deterioration of its qualities over time in manual transmissions and more frequently in automatic transmissions.

Transmission fluid generates a metallic clanging noise that gets louder as the speed of the car increases. The bearings and other moving parts of the box will run dry, resulting in a loud noise, if the level is insufficient.

This is not only inconvenient for the driver, but it’s also harmful to the affected areas. Because of this, it is essential to keep an eye on the gearbox oil level and viscosity at all times.

If you hear this noise, it’s probably because the transmission oil level is low.

  • The engine is still cold. Also here, the cause of the hum may lie in the thickness of the fluid and its contamination.
  • The car is moving, and the noise increases in intensity as the car’s speed increases;
  • The engine is idle, or the gear is in neutral;

Damaged driveshaft bearings

Drive shaft bearing failure is another major source of noise. Whether it’s due to normal wear and tear, the presence of a little quantity of oil, or dirt building up inside the bearings, this happens. There is a distinct sound:

  • when the engine is running at high speeds;
  • when starting the car and the engine is cold, the noise can be present in the engine at low speeds then it goes away.
  • when driving on a hill;
  • when the car is moving, but the hum disappears when the clutch is pressed
  • the noise is quieter at low speed and louder when you increase the speed

It’s possible that the first drive shaft bearing will be destroyed, and the second and third driveshaft bearings will be worn out in the first three scenarios.

Bad or worn gear synchros

transmission bearing noise-2

The gear synchronizers in the gearbox might also wear out, resulting in a humming sound. As the engine speed increases, a metallic clang can be heard.

Manual transmissions can be difficult to shift when the synchros are poor, and the gear shifter will have a hard time staying in the gear it has been picked and will set itself to neutral.

It is most likely that the bearing on the input shaft of a manual transmission creates a noise when the clutch is released and the automobile is stationary.

Front bearings take on a significant amount of pressure when the manual transmission makes a louder noise in first or second gear than it normally does. As a result, the input shaft bearing must be examined.

When driving on a slope or immediately after starting the engine, the input shaft bearing may create a noise. After pressing the clutch, a squealing sound can be reduced or eliminated.

This is because pressing the clutch stops both the primary and the bearing from spinning.

Rear bearings on the secondary shaft take a heavy load when the gearbox is loud in 4th or 5th. Even in reverse, these bearings can make a racket. The louder the hum, the higher the gear position. The hum will be loudest when in fifth gear.

A failing torque converter

Torque converters can be the source of noise in an automatic transmission. Changes in gear are usually audible when moving at a low speed, but the noise disappears as you reach 37 miles per hour.

Additional signs of a bad torque converter

  • The car jerks and vibrates when moving;
  • The car is slipping when starting;
  • You can feel the smell of burning in the cabin;
  • Wear of individual friction discs
  • RPM does not rise after certain values;
  • Depressurization due to destruction of oil seals;
  • Wear of intermediate and support bearings;
  • Low transmission fluid level.

Differential gears

The differential gears may also be to blame for the transmission’s squealing noise. They produce a metallic-sounding noise. This sign can be seen when the car starts to slide, although it normally appears smoothly and goes unnoticed by the driver. Uneven but high-torque rotation of the driving wheels is the result. This puts a lot of strain on the differential, which will eventually fail sooner.

When you start the engine, the car will roll back and forth. This is the best way to tell if the differential is failing. If you observe this, you should have the differential inspected.

Transmission noise additives

It is possible that additives can minimize transmission noise, but this will not be enough to cure the issue. A temporary remedy for noise reduction, they can also slow down the deterioration of your hearing..