B6 S4 prop-shaft noise and vibration

Audi 2003 B6 S4 V8 4dr UK saloon, 24,000 ish miles, orginal owner from new.
Following some recent work by a trusted local independant tech to replace a damaged heat shield above the prop-shaft, it has
developed a loud noise and vibration under acceleration. The garage did advise me when I went to collect the car, but he couldn't pin-point the problem.
At first, we both thought it might be the centre bearing - we raised the rear wheels free of the ramp deck and ran the engine in 2nd gear at tick-over - the tech said there was a slight oval motion about the centre bearing, but I couldn't detect any vibration in the drivers seat.
When I drove the car home, there was no noticeable noise or vibration at either constant speed or on over-run. There was however horrendous noise and vibration on acceleration. The lower the gear, and the harder the acceleration, the worse the noise and vibration. The higher the gear and gentler the acceleration the less noticeable the noise and vibration. In fact, in 4th, 5th & 6th, I couldn't notice anything at all. I found a quiet lane, and tried some stationary 1st gear stop-start-stops, and after a while, the noise/vibration seemed to clear. However, after reversing, and then driving forwards, the noise/vibration returned with a vengance, and I could not reduce the noise/vibration as previous.
The noise/vibration seems to be coming from the centre/rear area, perhaps under the centre of the rear seat, but it isn't always easy to determine exactly where, when you are keeping a lookout on where you are driving!
I'm not at all convinced it is coming from the centre bearing - because it is only noticeable under acceleration - if it were the centre bearing, then the noise would be there at all times.
I think it *may* be the rear joint. These are a kind of self tightening constant velocity (CV) joint, with alternating tapered ball tracks, which look like a "WW" when viewed from the end, rather than the parallel "I I I I I I" ball tracks found on axle driveshaft CV joints.
Has anyone else come across prop-shaft failures on Audi quattros?, and does anyone have any other opinions on my problem.
BTW - I'm not looking for pointing the finger and blaming anyone - the tech already thinks he knows he has screwed up - we are both just not sure what went wrong, although he did admit to have to loosen the rear prop joint from the diff pinion shaft with the assistance of a hammer and chisel!!
Thanks and regards
--
Sean
'06 Golf GTI 2.0T FSI, '03 Audi S4 v8, '99 Astra 1.8 Sport
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have used a puller to remove the pinion shaft, its probably bent now if its been bashed, hammers & chisels are only recommended for use on fords,
Steve.
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