[projectRDM]

Tension in the driveshaft rarely makes noises, and if anything it will slightly increase wear on the carrier bearing and the transmission output shaft seal, but that's it. Most cars have enough play between diff/gearbox/motor mounts to accomodate the added length. The sound you're describing, if it was driveshaft induced, would mean that there is too much play in the shaft, the opposite of your situation.
Ujoints are not replaceable on a Schassis shaft, so either buy a new one or start salvage hunting.