I've noticed that recently my A4 B7 has started making a sort of knocking/banging sound from the rear. It is only really noticeable at slow speed - mostly when stationery and then reversing or when going down an incline and coming to a stop. I'm thinking it must be a suspension bush somewhere that's knackered or perhaps an ARB bush?
Initially I thought it was the sound of the petrol moving in the tank as I read a similar thread that suggested this. However it seems to do it even with a full tank.