Thunk from rear going over potholes or bumps

[Slabber]

Okay, my garage (Audi independent specialist) have now given my car a thorough inspection and can't find anything wrong with the suspension, nor with anything else that might be causing the 'thunk' from the rear. They can hear the thunk though, which is something I suppose. I'm now considering having some rear suspension parts replaced on a speculative basis. Grateful for suggestions as to what to start with!