If you hear a loud knocking noise from the rear of the car while driving then there's a good chance the rear upper shock mounting plate is broken. We suggest replacing both rear upper shock plates at the same time because the other one is likely ready to fail as well.Google+
Car Problem Reports
Volvo 850 Broken upper shock mount may cause knocking from rear of vehicle
Volvo 850 Problem
Average Mileage: 152,333 mi (144,000 mi - 160,000 mi)
Visitor, 1995 Volvo 850, 144,000 mi
me too, i changed the shock first but found it was the mount
Visitor, 1997 Volvo 850, 153,000 mi
850 wagon. Replaced both at the same time. Accessed from inside car by lifting front cargo floor panel. Inexpensive replacements found at FCP Groton.
Had both of these fail, one at 145,00 and the other at 169,000. Makes a very loud noise from the rear of the vehicle when going over any bumps.