Replacing rear control arms

[Technomage]

I could tell something was wrong with the rear of my car because hear a noise in the car when I am going over 50mph. But I was at the mechanic this morning and he showed me (car was up on a lift) the wear on the arms/coilspring shim. My shim looked like it was cracking and the coil was almost coming out the shim on the right side of my car. He also showed me the wheel "jiggling" if you moved them around same symptom as what mrbmw explained. Basically if you jack up the car and try wiggle the wheel if it wiggles you have an issue, if it doesn't your good.