I have a noise in my rear end, if I grab the bed of the truck, and rock the body back and forth, I hear a clunk, almost sounds like a wheel is loose, but checked them, all good, also checked the U-joints, and pulled the driveshaft to grease the spindle. Thinking it could be in the third member, maybe the Differential pinion shaft, or the lock bolt......any suggestions, or help would be appreciated.

 

Check the wheel bearings.

 

Also check axle shaft end play in differential. My 1999 F-150 with 9.75" rear did same but never caused an issue for me.

 

Not making a growling noise, so ruled out Bearings, have it narrowed down tp the differential Pinion shaft has worn down.