This question may have been answered before, as found some threads concerning it on the a4 forum but nothing on the a3 forum.
Just bought a 2001 audi a3 1.9Tdi and have noticed when accelerating it makes a hissing sound. This is audible when you have the window down. It seems to happens at low rpm (about 1500-2500), it does not seem to happen when idling or when just revving the engine. Is it meant to make this noise?
Any help would be appreciated. Thanks