humming sound

Brandon Rogers brogers at
Tue Feb 25 08:51:53 EST 2003

My A4 (granted--wrong kind of 20V) has made "humming" sounds before--I guess
that's a good way to describe the sound, and it was the bypass valve.
Unfortunately I don't know how, if possible, to test the BP valve.  I just
replaced it and the sound went away.

'84 urq
'98 A4
20V motor on stand

----- Original Message -----
From: "Vincenzo Basile" <Bleaf1 at>
To: <200q20v at>
Sent: Monday, February 24, 2003 7:05 PM
Subject: humming sound

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Hi list
MY car is making an annoying humming sound when I am on the gas at a
moderate speed,but goes away under hard acceleration,while my clutch is
starting to slip under high boost I do not think this hum is coming from my
throw out bearing(but not sure).I had a mechanic friend in the car and he
thinks the sound is coming from a bad turbo bearing,what I'm wondering is
how can my boost still reach 1.8 and how do I check if it is the turbo.

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