I have had a loud chattering sound at crawling speeds for a while now. I finally took it to a jiffy lube and drove it back and forth over the bay and the tech told me the rear u joint was chattering and vibrating. I have cut the springs in the back and lowered it down about an inch. It has new U joints on both ends and balanced shaft. I already got an adjustable panhard bar but do I need adjustable control arms too when I lower? (could the lower body change the angle of the joint?). Could someone tell me what kinds of things could cause this chatter?

Thanks
Matt