hard vibration when in a high torque reverse 1998 xc70

[toolmaker10622]

Car developed a bad vibration/sounds like bad u-joint noise when I back up hard. Back up slow/moderate, it's fine. Car runs great in forward.
Took the rear drive shaft off because it seem to be coming from the rear of the car. Noise is still there. Wondering if
bad front axles could sound like this at the rear of the car?
Also, where is the viscous coupling located on my 1998 xc70 Cross Country? Thank for any help.

[pokiarchy]

My first guess would be motor mounts. I'm not too familiar with Volvo's in particular but I had the same problem with my Mercedes and it was the engine mounts/shock. Although if it's definitely coming from the rear, it could be the bushing your shock is sitting on top of, if you jack up the rear end you might be able to tell if the shock has too much play, or check the strut mounts.