This is exactly what mine was doing and yes it was the plastic rack that holds the roller bearings. I am glad I fixed it before it completely ruined the front differential. It was over $230 for just the plastic cage and they wanted $5 a piece for the roller bearings which mine where still good. This fixed the problem completely !Inside the front diff there is a plastic "rack" that holds 12-14 rollers. They are know for the rollers detonating causing them to split in half and doing serious damage inside the diff. The main ring gear inside the diff has a large bearing that seems to bear the grunt of it in my experience. The rollers are 240.00 to replace as long as the rack that holds them is still in tack. The diff is very straight forward to take apart to inspect bearing damage.