Severe vibrations when doing U turns
 

I have a 2016 Model S6 with 15K miles. When I execute slow U turns in any direction there is severe vibration and grating sounds that I can feel and hear. The Audi technician says its a designed in feature that has to do with the way the differential is designed to work and that this occurs on all Audi S6 cars, and other Audi's that have a sports suspension. Has anyone experienced this, and more importantly have you found a solution?

Audi Quattro models don't particularly like doing 'full lock' turns, including U-turn type scenarios. The longer the wheel base, the more pronounced this becomes.

If you back off the lock slightly, does it get less severe?

I wouldn't classify the vibration as severe, but some binding in sharp turns is normal for a car with a Torsen or Crown-gear center diff. Nothing to do with the suspension.

Do you have the dynamic steering option? In the manual it says its normal to make noises at low speed and full turn.

'totally' normal and like mentioned, quattro. In a way i do think suspension also comes bit in the play, not directly but the stiffer the more it will translate (R8 for example is even worse at sharp U turns).

Wheel size
 

I get vibrations and noise with my 20"
wheels but much less (almost none)
with the 19". What size wheels do you have?

Recently, I changed the fluid in my center differential, & it DID reduce/eliminate the binding noise/vibration on tight slow speed maneuvers. It's an expensive "buy from audi" fluid. Mine is an '06 C6 quattro(torsen).
I do have to give credit for the good advice that I got to do this on this forum.