New noise in 4wd....

[the evil twin]

snip...
It started out as a light growl (about the best way I can think to describe it), didn't make the noise when accelerating, only when coasting.

Once we hit the blacktop and back in two wheel drive, the noise went away. I then tried driving with the lever in 4 high, but not locking in the hubs, and there was the noise, I also tried driving in 2wd with the hubs locked, and there was the noise again....

Well, there's growls and there's growls so without much else to go on...
I would hesitantly suggest it is possibly an outside chance of maybe being a universal joint or a CV.
When they first start to crap 'emselves they can go quiet under load and only get noisy when coasting.