Strong jerking during load change

Hi, guys.
I got a problem with my buddy's S6. Car's a V8, 6 gear, Bj. 95, about 215tkm.

To the problem:
when changing loads comes a rupture banging from the rear axle, you can feel that in the whole body.
I've already changed the cardan shaft, gear bearing and the bearings from the longitudinal handlebar (is that what this thing means? Sits near the threshold). All the other camps look good, not a game. The game in Diff is also not worth mentioning. I checked the throttle flap pot, too. Which is not what it should be.

If the car bought about 3 months ago, I didn't notice it (the wheel bearings were also so scratching, I thought I was driving a tank). Wheel bearings are now new, brake pads at the rear too (made by a free workshop).

What else could be the cause of this banging?
Maybe they did something wrong in the garage?
I checked all the screws and so on, all right.
I don't want to change everything on blue haze, because at some point it goes into the money.
Oh yes, the seat heater driver side is not working either. Can you measure the heating mats? If so, what values do they have to have?

I am grateful for every tip!

Greetings to Dominik