Moan in T/C or Diff?

[WhiteWhale]

I have a moan and was not sure if it is coming from the transfer case or rear end. Is there any way to tell one way or another? T/C is an NP205 and the PO used ATF as lube, the rear is a HO52 with new wheel bearings. Both had bad output shaft seal leaks which I replaced but figured both were probably run low on oil at some point in their lives.

The moan itself comes in only above 45-50 mph only under load or light load.

Thanks