I have a 03 f150 7700. I just replaced all the bearings in my rear diff and was told that my gears were good and didnt need to be replaced. I drove my truck home that night and found that it was making load whinning noises when stepping on the gas. It almost goes away when i let off the gas and is most promounced when Im at about 50 to 60 kmh. I took it back and they told me that i needed to replace my rear rotor and this cound would stop. This does not sound right to me . I was wondering if anyone would have some insight to this. thank you

 

It is more then likely your rear diff\LS making that noise. Common issue on our trucks. Check out the thread right under this one for some information. Mine does the same exact thing at 40 - 50 mph.

 

thanks for the response, but my truck is whinning at all speeds. and almost onlt when i push the gas. I am taking it back in on friday to have the brakes done. witch the machanic is sure will fix this issue.