Vibrations rear axle

Hello, community
Have a new question.
I have recently seen vibrations from the rear axle between 30 and 60 km/h on my S6 Avant
Over 60 is all OK also 200 is problem-free
They always occur when you are stupid and sometimes also downhill in thrust operation.
First of all, a fundamental question:
Are differentials or drive shafts often damaged at the rear, which can cause such vibrations?
I shut out windows, because everything is quiet when braking.
Any other guesses??????