check the wheel sensors.....It might be the ABS sensors are dirty... I have heard of this problem before and it is usually due to the fact that one of the sensors is dirty / blocked and the other one fine.... hence the braking effect...
remove, clean and re-install the sensors / connectors..
I just noticed this noise on my 1998 A4 Avant yesterday. Can anyone confirm that it is the sensors? If it is the sensors, where exactly are they located? Any help would be greatly appreciated.
Yeah it is probably loosely replaced or dirty sensors. Does it feel like a shudder or viibration in the pedal. Kind of sounds like farting?
In the front of the rear rotors and behind the front rotors, there is a wire coming off the ABS computer to a head (but not a brake hose (know the difference)) It goes into a head (black plastic) with a magnetic cylinder maybe 5/8in diameter on the rotor end. On all you guys with the older 98 and 97s it(the head and magnet) just slides in and out. If it was never cleaned it will be a little work. Get something with a soft grip head and get a good grip on the cap and twist it loose (like battery cable removal- no prying) Well you should start with just using your fingers, but if they dont work, I used vice grips on a shop rag. Audi has a tool, but they could not get mine. Anyway, your sensors may set off the check engine or ABS lights if they are dirty and will eventually burn up (160 parts/ wheel). Oh yeah after you get it out, wipe off the crap, wipe down with a little oil (to make it easier to pull the next time). And uh, on the newer ones, I hear the cap is a locking ring kind of thing so twist first before pulling. And uh don't break one, it could be bad.
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