Audit TT ABS problems

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I’ve got an intermittent but daily problem that I think is ABS related. ABS light comes on sometimes, but so does a clunking, sometimes grinding type noise from the front end when moving forward at low speeds. This is a 2000 Quattro model, manual shift. Dealer replaced one wheel sensor ($400 parts and labor) and says car scans fine, no safety issues. Problem continues, same as before. Took mechanic for a drive and of course I could not get this to happen. Happens all the time though…anybody got any ideas?