Rady, it definitely sounds like the ever-popular rear sway bar. I will listen when you come up here next week. Mine used to do the same thing.
If anyone wants the bushings, let me know. If someone other than Randy wants them, I will "share the wealth". Otherwise, he is taking the springs, struts, and bushings next Tuesday.
Derek, I found the S4 that I wanted but we were about $900 apart on price. It was at a dealer and they were really trying to screw me. Basically, I am looking for an 01 or 02 with around 40k miles. Would prefer silver, blue, or black; not really into the flashier colors like yellow or red.