AUDI?? Maybe you are a bit off-topic; out here only Italian freaks, so be
careful what you say (or write)!! Wish you well.

Not a good idea to post Audi problems to a Fiat group. Some clunks
are well tightned bolts of the wrong size. Some bolts are straight
shank, only threaded at the end for the nut. These are a close fit
and rust in place, locking them solid, so some dipstick of a mechanic
undoes them with an airline impact driver, and not having the correct
replacement puts in a corresponding size all thread, which is smaller.
Tightens it well and all seems fine, until eventually it starts to move,
Result a total pain in the arse to diagnose clunk. Also are you sure
the rack isn't intermittently moving and that all of the cone and
taper ball pins are tight?