Sounds like a bad rear shock mount. Had to replace them on my 95 850. Banged going over bumps. Good news is it is optional to replace the shocks themselves as 850 rear shocks last almost forever! Not so the mounts… How many miles on your car? You will need to move the shocks out of the way to access the mounts so you might consider doing both especially if you plan on keeping the car for awhile.

Also worthwhile checking out the rear suspension bushings before jumping to conclusions. Both rear suspension bushings and rear shocks rarely wear out.

Will I buy another Volvo??? We'll see....