Thumping noise
 

Hello,
I own a 2006 A-3. For the last couple of days a thumping deep & soft noise ( (is not loud) comes from the rear of the car. It comes and goes & one of those days I did not hear the noise. The car runs fine. At the local VW shop they said it might be the exhaust. I planning to take it to Audi Friday. I can hear the noise while driving and stopped.

Any ideas of what it might be ?

Leo---