My guess is one or both of the rear axles are a little bent. If you remove them both, you could remove the driveshaft and turn it manually to verify that the differential is working smoothly, which I suspect it is.
My guess is one or both of the rear axles are a little bent. If you remove them both, you could remove the driveshaft and turn it manually to verify that the differential is working smoothly, which I suspect it is.