Just picked up my A6 a few days ago and what a car! :-)
I've just noticed that it has an annoying exhaust vibration at the drivers side, at the tail end.
Sounds almost like a 'tinny' vibration if you understand what I mean.
Seems to be fine on the other side though.
Not the worst sound in the world and it can only be heard when you are out of the car but I guess when you know it's there, you want rid of it!