I have this whining noise that comes and gos on my 06F150 FX4. I hear it more at higher speeds and when i slow down to a stop it gos away. At frist i thought it was some thing in the tranny but now it sounds like its coming from the rear end of the truck. The truck only has 5200 miles on it and this noise is driving me nuts. Help any ideas.

 

Not to ask a dumb question, but have you had the gears in the diff changed? I just did and I have the same problem you do. When you're on the gas you don't hear the whine, but once you let off, it starts. As you start to brake and slow down the noise disappears. Yeah it sucks. Our you could have a bad bearing. Pre-mature failure.

 

Sounds like a case of old fashioned gear howl. Check to make sure there's the proper amount of oil in the diff, and also make sure it's the right weight oil. When I bought my '04 Ford recommended 75W90 gear oil, they've since changed it to 75W140 to cure the issues that people were having. If it's limited slip make sure it has the right amount of friction modifier. Those two things should cure your problem.

 

did you mod the truck in any fashion before the noise started?