what do y'all think would cause a whining noise between 40MPH and 50MPH, only when my foot is on the pedal. if im coasting no noise. sounds like it comes from the rear of the truck. I don't guess its a wheel bearing. that would be constant, i think.
Differential getting wore? Diff fluid was changed 1 month ago and is full, no signs of metal in the fluid or excess wear. Trans fluid is full....
no other issues.

 

Does the pitch go up and down with the gas pedal when the noise is heard? If you have a carrier bearing for the driveshaft check that. The pinion bearing is going? If it is the pinion bearing and you don't mind the noise, they'll last another 50k or more. Without the truck here its a guess.

 

It does change pitch somewhat, but not very noticeable. it loudest at 45MPH, then disappears at 48+ MPH. no noises at 55, 60 or 70mph.
I'll try to get a recording of it.

 

Roll down your windows and open your rear sliding window while you're at a complete stop. Go from Park to reverse and neutral to drive and listen for any unusual noises or have somebody under the truck. Also jack up the rear end chalk the front wheels and slowly rotate the rear end while listening for noises. Is there any rough shifting as well? When these trucks get into really high rpms in the early gears they can make a good bit of noise or you're just paranoid. 🙂

 

Only Caveat is my windows don't work. No rear sliding window on this truck either.
However i have been outside the truck with the someone going from P,R,N and D and there are no unusual noises, i jacked up the rear end when i changed the diff fluid to see if i had a limited slip or not, and i did spin the wheels and i didn't hear anything abnormal.
Trans shifts smooth as butter.
this truck has zero weird noises or anything,except for this whine/howl from 40 to 48-50 MPH.

 

Send it and if it gets worse then odds are you'll know 100% where its coming from. Only other suggestion would be bring it to a shop or if you're feeling brave enough lift the truck up and go underneath while someone is on the pedal.

 

And have them apply the brakes some, to put a load on the driveline.