I spent an hour under the truck yesterday. Checking everything from front to rear. All the things you mentioned are bolted down tight. Rear shocks, rear swaybar ends links and the brackets mounted to the axle, lower control arms, upper control arms, and panhard rod (an adjustable one from Sonoran Steel). Nothing is loose. I couldn't do anything to make noises that resemble what I hear until I sat under where the spare goes, grabbed the frame and began shaking it side to side. Immediately it starts with the noise. I can feel it when placing one hand on the either of the backing plates and shaking the truck with the other. It certainly seems to be coming from the axle.