Kind of a ticking sound but not exactly, sort of like the sound a bad lifter makes but more smoothed out, if that makes sense. The sound is usually constant at high speeds only when the accelerator is pushed.
I'm pretty sure that it doesn't make the sound when I'm parked and rev the engine.
Could it be that there's not enough lube in the dif? The guys that installed my gears really screwed me over once by not installing a new crush sleeve, wouldn't surprise me if they messed up somehow with the gear oil level. Maybe I'll put in some Royal Purple.

Stefan Doerr
'94 Trooper LS
6.5" lift, 33's, G80 and other stuff
http://community.webshots.com/user/smd94trooper