Horrible transmission sound

Hi Guys, wondering what people think. I've had a sound coming from the drive train for some months that has slowely been worsening it occurs when I back of the gas particularly when I've been driving at high speed. The sound is like a vibration/rattle/zzzzes sound like a loose bearing or worn bushin or perhaps UJ thats occurs when the parts loosing speed so not centrafuging. It seams like its either in the front diff, prop shaft, or transfer or front end of gearbox. I at first thaught uj so swapped to another used spare prop but this did not solve it. I think in the morning I will drop of the front prop and take it for a run to see. I'm contemplating taking the gearbox and transfer off to take a look deaper or swap for another. Before I do this any obvious ideas, I have a 2" lift could it be I need a double cardin prop? Or does it just sound like knackered gearbox or transfer. I cant help but lean towards transfer, any thaughts thanks Jim

is there any freeplay in diff flanges ,noise on overun is often worn diff pinion bearings ,removing front prop may help to diagnose

Thanks JM sounds like a possibility, I will pop of prop today and check out. That would be a reletively nice soloution as I planned to rebuild axles anyway. Saves getting the gb+transfer down again!

Well removed front prop, locked CD and have been driving around all day in 2wd. Sound gone so hopefull its the front diff. Will swap diffs on friday to see, will be a bonus if this is the soloution as I only swapped the gearbox/transfer (to another used one) 6 months ago so a bit anoying to have to replace it again. On a side note is it ok to drive the car (with prop removed) and CD locked. I never normally drive for so long with the diff locked, it really does show the apparent where in the cd when it is locked. Something you notice less when I lock it off road for a few km. Thanks J

yes its fine to run on rear axle with diff locked ,but obviously all drive is now on one diff not 2