Hello men, have not posted for awhile. I have a 2000 f-150 with 115,000 on it and a 10.5 rear-end, a few months ago it started making a whining noise in the rear area. The pitch does not change as you go faster it just gets louder and louder the faster you go to a point where when u are going 60 mph you know its there but it appears quieter cause u are going so fast...(sounds like i have big off road tires but not as loud) you can really hear it at 20mph!!! The whine is noticeable as soon as u pull away and the faster you go the faster th noise goes so at 60mph it seems allmost gone(get it??) Its not the tires!! I checked that...do think its the u-joints?? they feel ok to ME. I changed the fluid with ford stuff and trac lock mod. When u shut eng off while coasting in neutral you can open doors and hear comin from center of rear not one side or other so im thinkin not axle bearing. its never been run dry or low on fluid.
I tow a rv 6-7 x's a year with it and the truck bed fully loaded. please tell me this can be the u-joints...i'll prob change them anyways, just tryin to get some help on what it may be...I'm hopin I will not have to open her up!! I guess that would give me excuse to get 373(have 355 now)...... .thanks

 

My brother's 92 flareside had a problem similar, ended up I think to be the carrier bearing or something else like that, long story short he needed a new rear. Fix yours early enough you may be lucky. Do you have an 8.8" or the 9.75" rear, his was the 8.8. Hate to tell bad news but hopefully it's something small. Either way, have it taken care of quick so it may stay small. Good luck.

 

Hopefully it is a U-Joint and not a bearing.

 

Either the carrier bearings and/or the pinion bearings need to be replaced. Our V8 Mountaineer had the same problem at 106K miles. Costs 300 hundred bucks to get them replaced, including parts here in Alabama. Unless you know how to set preload on the bearings, you're better off taking it to someone else. I found a 4X4 shop that knows what they are doing. Find something similar in your neck of the woods. Good Luck!