its a 2000 agu, drive by wire. on the over run you can hear a knock. ive been over the engine with a stethoscope and at first it wasnt clear where the noise came from (not bell housing, not exh. man. turbo area, not the crank case) the aux belt tensioner moves with the engine revs and it doesnt move smoothly as ive seen with other engines, it looks jerky im planning to get the aux belt off and see how this effects the sound anyone experienced the aux belt tensioner creating a knocking (high freq, varies with engine revs) sound before?