The lesson I learned... Check your panhard rod. I put poly bushings in mine a year ago and lo and behold they needed lubbing up. Dammit. I changed shocks, visually inspected everything, lubed my endlinks, rear swaybar bushings, and my rattling problem in the back just kept getting worse. I was embarrased to drive people around and didn't want to cave in and pay 900 bucks for a mechanic to fix it.

Anyway, I'm thrilled to figure this out... I forgot the cardinal sin of Poly, it needs to be lubed occasionally and if you experience noise going side to side in the car, it can be the panhard...

 

Amen and pass the axle grease!