Hi I had the same thing on my A6 which is not that different with how it works, my educated guess is its the engine and gearbox mounts, what happens is the engine mounts are Hydro mounts which are filled with oil and controlled electronically and stiffen up when stressed, the problem is they wear/split and the resulting vibration and movement knocks out the gearbox mount which is bonded rubber/metal, I got all three mounts on line from carparts in motion and if you ring them they are very helpful and what you want is listed normally on eBay and a damn sight cheaper than Audi, all the parts I bought were Febi and all movement ceased, I use the car as a cab and done over 9k since fitting just before Christmas and had no problems.
Steve.