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My 2003 Passat B5 TDI with 6-speed gearbox is making a buzzing/whining(?) noise while driving and it appears as if it comes from under the gear shifter.

The noise is:

  • Dependent on road speed (more audible between 60 kph and 120 kph)
  • Not dependent on engine speed
  • Also audible when gear is in neutral
  • Not dependent on clutch being pressed or not

When accelerating, the noise is there but less audible (probably because the noise of the engine masks it). It is much more audible in neutral or in 4/5/6th gear while decelerating.

Also, when the car is in 4/5/6th gear if I gently press the gear knob up (in 5th) or down (in 4/6th), the noise gets worse.

You can hear the noise in this audio file: http://goo.gl/qXX8x1

Could someone help me diagnosing where the noise is coming from?

I'm ruling out clutch and gearbox because happens in neutral and is not dependent on engine speed. Is this correct?

Could it be the differential? Could it be the U-Joint? Drive shafts?

altosaxwannabe
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2 Answers2

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While it is difficult to diagnose car sounds over the Internet, I would say pretty confidently that the sound is coming from the transmission for the reasons below;

You have stated that the pitch of the sound follows the speed of the vehicle, which would lead me to believe this is specifically the final drive or 'differential' (inside the transmission on a transaxle) rather than a specific gear that is causing the noise.

If the vehicle is moving, the final drive is moving. Specific gears or neutral makes no difference.

Under acceleration the output-to-final drive gears are meshing on the 'leading' side of the teeth, which makes a specific sound. Under deceleration they are meshing on the 'trailing' side of the teeth which makes a different (usually louder) specific sound. The sound is created by the two gears being too far apart (like tenths or hundredths of a Millimeter) - see 'backlash' http://en.wikipedia.org/wiki/Backlash_%28engineering%29

Different car speeds (and thus, frequencies of the gears teeth meshing) will increase and decrease the intensity of the sound as it passes through different 'Harmonics' - http://en.wikipedia.org/wiki/Harmonic. Around 90kph (55mph) seems to be a fairly common speed to hear intense harmonics, which is right in the middle of your 'more audible' range.

Pushing on the shifter can preload things inside the transmission and by way of transference is pulling the aforementioned gears apart increasing the backlash, thereby increasing the noise.

The final drive is usually close to the middle of the car, near the shifter.

Nick G
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Finally got confirmation that the noise is coming from the gearbox so it's either output shaft or (more likely) differential bearings as this is a common complaint for this 6 speed gearbox. Will have to get it repaired at a transmission specialist.

altosaxwannabe
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