A4 1.9 Tdi

[lowtherc]

My car makes a distinctive 'droning' sound around the 2000rev mark for
a range of about 100revs. I have had it in to an Audi main dealer, and
they can't diagnose the fault. I've also had it into to a number of
independant garages, who have changed exhaust compenents and even the
rubber mountings of the gearbox !! All to no avail. Can anyone shed any
light on this problem ??