The differential. Turns even when driving. While turning the tire on the outside turns more than the inside tire. Something is wrong in there. When it breaks it's all about a tow truck for it to get anywhere. Another thing, check and make sure all the lug nuts are tight. loose lug nuts can make a similar sound.
The limited differential is slipping. On some models this is normal. Take the cover off & check it out. It could be that it needs a additive to help the clutches work right. The dealer can tell ya if a additive is required.