Hi I bought this A3 Quattro 2.0TDI 2005 at an auction and it has some vibration at high speed 60mph-80 ish, its only in 5th and 6th gear around 2000 rpm and to around 2700rpm its also a sort of booming sound... it fades at around 80mph anyone got a clue? it's beneath the backseats...

 

Hiya Sotka,
did you sort your problem out cos ive got the same car as you but 2007 and it has the same problem?

 

check the tires and the tire wear ----- a3 tires have a tendency to feather, which can cause those symptoms ...