[rwhite692]

Boy... it could be so many things. What work has been done recently? You mention "everything underneath is new/tight"...

It's intersting that the shop thought the sound was coming from the body, and not from the driveline...I know you have said, "everything is tight", but I would start checking for loose fasteners. Just for starters:

Did you check the condition of the u-joints? If they were recently replaced, did you check that the u-joint retainer bolts at the yoke @rearend are tight (be careful not to over-tighten them!)

Did you check to make sure your leaf spring-to-axle u-bolts are tight, etc?

It's really hard to say where to concentrate your efforts, without more specific information...