My 97 F-150 has developed a whine and I'm not sure where it's coming from. It seems to be worst at about 40-60 mph and while holding a steady speed. It stops if I let off the accelerator or if I accelerate. Does anyone know what this might be?

 

Usually it is rear end gears(Ring & pinion). Bearings make more of a roaring noise especially at higher speeds. If you have a center support bearing on the drive shaft, it could be the culprit, but it more often than not makes a "ROAR" instead of a whine. The clue is that you say the whine is gone when the gears are under a load. Next time you get a chance, run it about 60 and just barely back off the throttle, just enough to un-load the rear end gears, but not quite enough to where engine drag is slowing you down. See if it is much more quite. If it is it's probably the gears.

 

Sounds like it may be your rear end gears making the sound.

 

that happened to my 98 when it had 400 miles on it. Started making a horrible rear end noise so i parked it at the dealer that night and went up there the next day. the shop manager started being a smartass about its probley packed snow or something. He went in pulled off the rear end cover, and it was dry as a bone.It came from the factory with NO GREASE so under warrenty i got a brand new 355 rear (around 2000 dollars) check rear oil level to be safe !! lol
Patrick

 

My truck is approaching the end of it's factory warranty and I took it in this week to have the rear differential looked at. It had a slight whine at about 45mph if I let off of the accelerator. The dealership replaced everything in the rearend with the exception of the axle housing and axle shafts. They reported that the gears were "pitted".