Need some help in diagnosing this problem. Its an 05 expedition 4x4 5.4 liter. The noise all of a sudden just started. Its a very loud creeking noise and sometimes will bang. Its coming from the right side rear of the vehicle. I have fixed the emergency brakes (were not retracting), I dropped the driveshaft to check ujoints and have added limited slip additive to the rearend (thought it might be the clutches in the rearend). The noise in intermitent and can be going straight down the road on smooth surface. It sounds like when your trying to take a rusted nut off a bolt, that loud creeking noise...Any thoughts of what else I can check. The vehicle has 85k miles on it...Thank You

DOC

 

I drained rearend fluid and replace with new synthetic plus the ford Limited slip additive.
Noise went away for the first 50 miles but now is back. Truck is going to Ford. Looks like something wrong with the clutches in the Rearend.....

DOC

 

Try a second bottle of additive. My dealership uses two bottles in higher mileage vehicles. It has worked for me without issues for 45k now. A $5 home fix as opposed to a dealership trip is always good.