My truck has a low speed driveline squeak (squeaky rubber sound) and some weird clunks. It also makes some weird noise when going down a hill in second gear (6sp manual) while using the engine to hold it back. I suspect the rear U-joints so checked them out. They are the origional U-joints (35000 miles) and seem OK but appear to have thrown some of their grease out. The only troubling thing I found was the amount of play in the tailshaft of the transfer case when I push up and down on the drive shaft to check out the U-Joints. How much play is normal here? and could the squeaking sound come from the little rubber dust shroud on the tailshaft housing? Any other ideas?