Mechanic Question???
 

You ever drive behind a vehicle and notice the rear wheels are riding out of alignment with the front wheels??? Like the frame is bent or something??? What causes this? Is it a bent frame? Car been hit maybe? I was driving behind a brand new Volvo today and it looked like shiiiite!

"Crab Walking"
Could be due to an accident, or rear axle alignment problem.

a frame condition call diamond would cause that, but only on a full frame vehicle.(Trucks, older cars, ect... where the body sits on body mounts on a heavy steel frame)
A Volvo is a unitized body, meaning the body and frame are one (all sheet metal welded together )
Pretty much impossible to have a diamond condition with a unitized body.
Most likely alignment problem or suspension sub frames either damaged or mis aligned.
This is more a body shop question than a mechanic question.

I agree with Ron..More than likely an alignment problem