2011 f250 4x4 6.2 


Got a head scratcher for me at least. Used to be a diesel mechanic do all my own maintenance have full toolset. Have done everything from engine swaps to oil changes. 

125k on truck, has a howling noise that has gotten progressively worse over the months. 

Things I know. 

Only during load/acceleration, if you are driving and release pedal noise stops. 
Does not make noise in neutral at any speed. Does not make sound at park or idle. 

Obviously wheel bearing was eliminated as coasting produces no noise and wheels/hubs have zero play. I drained and filled transfer case fluid was dark but not horrible no metal. Transmission fluid was perfect, dropped pan no metal, changed filter. All u joints are fine.  
My next thought we pinion bearing but mileage and no pinion seal leak led me to believe otherwise but I drained rear diff  removed cover  and resealed, no metal and gear oil was fine. 

I took it to a shop and we put it up on lift and brought it up to speed and it was screaming, the owner got stethoscope out and said it was pinion bearing 100%. He changed it and noise still there. He weaseled out of accepting blame for misdiagnosis on it citing a small 1/32 area of pitting on race lmao. I specifically told him I do not want to just throw parts at it I can do that in my driveway. Anyways 1800 bucks later to him and whatever I’ve spent on fluid changes here I am. Anything I’m missing? Any suggestions? I’m using this thing for my business and need to get it dialed as it is my work truck. I will include a video of the noise from cab. You will hear it stop when stop pressing gas. 

Any wizards wanna help me with this HOWL/WHINE