When I did an oil change at Sears, I had them check the diff fluid. They didn't put the plug back in the rear correctly, and it fell out somewhere, and inevitably, I didn't find it until I was giving the underside a once over AFTER wheeling in ddep water. I took it back to Sears and they refilled the gear oil and put in a new plug. After time, I started hearing something like what you are explaining. I took it to the dealer (it was under warranty, obviously before I lifted it), and they said it looked like the rear diff was full of water, They fixed it under the warranty, but that is what caused my problem.