A4 FAQ: 1.8T Moan/Groan-Like Noise

Written by: Tom Fric in 1999
Please direct specific questions to the author!

There have been a significant number of A4 1.8T (with manual transmission) owners complaining of a moan or groan-like sound coming from the engine area under acceleration. The following symptoms appear to be typical:

  1. Noise occurs between 2000 and 3000 rpm under slow and moderate acceleration.
  2. Noise lasts for a short time - a split-second to a couple of seconds.
  3. A slight vibration can be felt through the gas pedal or floor.
  4. Noise tends to occur more often as the outside temperature is hotter.
This solution for this noise is known by Audi, but not all dealers appear to be aware of it. The noise is an acoustic resonance having to do with the turbo bypass hose system (similar to the noise you get when blowing over the top of a Coke bottle). The fix is to replace the bypass valve hosing and thereby change the placement of the bypass valve. Apparently the fix involves replacing the hosing of the manual's to that of the automatic transmission's. In three documented cases in A4.org, the following parts were installed during the fix:
  • 1 058-145-712-A Pipe
  • 2 N-024-504-4 Clamp
  • 5 N-101-965-02 Hose (in 2 cases), 1 N-101-965-02 Hose (in 1 case)
  • 2 N-102-581-01 Clip
  • 1 058-145-832-C Hose (in 2 cases), 1 4B0-145-832 Hose (in 1 case)
  • 1 035-133-989-A Adapter
  • 2 N-100-911-01 Clip

The occurence of this noise and its related fix have appeared on 1997 and 1998 model year 1.8T's.

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