While at the dealer with my F350 Dually while doing the NOX update, I mention a rattling sound while backing and turning. Also, could feel rear end ratchet when making a sharp turn such as into a driveway.
DEALER found a FIX! There is an updated rear end from Ford for this condition that replaced the factory Dana rear end. In the 125 miles or so I had the truck back before the check engine light came back on after the NOX update, the replacement FORD rear diff was much quieter and smoother! Yeah!
I think the deciding qualifier was if it has the "camper" package with the underbed supports. Not sure what that has to do with anything, but it seemed better.