I recently purchased an A3 2.0L TDI 140 Sport. On purchase the car i could honestly say sounded and drove perfectly.
As weeks have gone by an unusual whistling noise can be heard, but it goes when you rev the car. If you leave it ticking over it is that loud its irritating. Also when you rev the car you can faintly hear what sounds like a dump valve dumping.
From outside the car i have pin pointed the noise to the top of the fuel tank. So I have removed the rear seat and panel to view the top of the tank, but it is louder from the outside of the car.
Only thing left to do is remove the fuel tank, which i am leaving as a last resort.
I have not got vag, so looking for advice before i pay someone to plug her in.