I have a 2005 Ford F 150 4 X 4 XL with a 5.4 L with 185,000 miles.
I have a whine coming from what I believe is my rear axle/differential. I had the clutches replaced a few years back. Now I have this whine. It is not a gas driven noise, its louder as you go faster. I removed the driveshaft put it into 4 wheel drive and drove it. Noise still there and it in the back. I don't know what it would cost to rebuild and that scares me. I tried put it up on jacks and got underneath with a stethoscope. I could not pin point the whine. I am considering going to a pull a part junkyard and getting a rear axle. Around here they are around $100. I know the you get what you pay for deal but I don't have the money to fix the one on the truck now. I know it has a 9.75 Differential. When I am looking for a rear end what specifics will I be looking for? What years will fit into my truck? On another note: When I removed the driveshaft I found the Noise Dampner out of alignment and causing vibration. I have removed this steel ring and it improved visible vibration. Any ideas, suggestion, and help is much appreciated. I am mechanically capable but not to the extent of a rear axle rebuild.
Thanks,
Scott

 

Could be a tire noise. Have you tried moving the rear tires to the front to see if the noise moves with them?

 

I had the exact same thing, same year, and 182,000 miles. Mine was also a 9.75.I took it to a local mechanic and he put in new pinion bearings, my larger one, closest to the differential was visibly damaged. The race had pits in it caused by ?????? maybe heat?, or maybe just wear.
First clue was I pulled the oil fill plug, and found it loaded with metal slivers. I drained the oil and ran a magnet through the oil, which to my surprise was not loaded with shavings like I had anticipated. The mechanic said the inside was really clean and my other bearings looked like new, it was just the pinion bearing causing the issue.
He mentioned that the 8.8s sometimes wear on the outside axle where the axle rides on the bearings, and this sometimes causes noises.
If you choose to get another rear from a salvage yard, make sure it is same gear ratio.
My repair cost me $590.82. half of that was labor and a new set of parking brakes, because it was somewhat labor intensive. If I had it to do over and knew for sure that was what I would find, I would have done it myself in my driveway. I was just afraid I would get it apart, and not have a way to get it back together to get it to a shop.