Bad U joints or driveshaft?

I have a problem after my 4WD is engaged (NP231). There is a banging sound coming from around the front passenger side area I think. Just started this morning. The banging gets faster as I accelerate more, but it doesn't do it constantly. It's fine in 2WD. Some kid at work said it could be the U joint, and that the added torque from the 4WD could be causing the noise, or possibly the driveshaft from the TC to the Diff could be the problem. How could you check either? Any ideas?

Could be either or. Could be a chipped ring or pinion too. Just pull on one side of the axle and also try the drive shaft wiggle it back and forth. If theres any play find out which joint has play and replace it