Yea, that would help...If it moves around normally in 4Hi or 4Low, that would seem to rule out the transmission which is what the OP should be hoping for, unless he doesn't mind pulling everything out and going through the trans himself. He also needs to scan the PCM for chassis (Transfer Case) codes. Those will NOT illuminate the check engine light. There's still an outside possibility its the encoder motor assembly mechanism (codes will be stored, if so) or even rear end but slim based on what all has been shared thus far.
If the trans is in D or R, T case in neutral, vehicle will simply be in neutral with no extraneous noises.
These cases (no pun intended) are always tough to diag over the net but hopefully a bit more info can at least pinpoint at a high level where the problem is (assuming it's just one major component that's bad, and not multiple)...beyond that, doesn't really matter...