STRANGE "GROWLING" NOISE AND VIBRATING AT ACCELERATION

[Oostenstein]

I own a 2020 GMC sierra 2500hd SLT 4wd 6-speed automatic 6.6l V8 GAS crew cab.

At roughly 70,000 miles it has started making a strange growling/buzzing noise that sounds like its coming from the under carriage, under the passenger side floor board.
It kind of power surges my truck and feels like its "jolting" when it does it, but Then it goes away. 
Seems to start mostly around 45mph at minimal throttle but it goes away instantly when you left off the throttle.

It is completely random when it'll do it but mostly when I accelerate, or at higher RPM's or speeds.
At first I thought it might be the transmission, transfer case, or something grinding between gears. Then I thought it was a heat shield rattling. No luck. 

I took it to a mechanic and they thought it was my muffler, so I had a brand new car back exhaust system put on with a new muffler.
They also thought that it might be a u-joint in the driveline that was starting to seize up, but after inspecting everything they havent had any luck.

My Mechanics pulled the rear driveline and checked u-joints. left the rear driveline out and even drove it around in 4x4 to see if it was out of balance or vibration was still there. Noise continued.

They balanced and rotated the tires and still the same.
Its driving me nuts! The noise has been an absolute ass kicker trying to track down. No luck pin pointing it yet. 

Has anyone experienced anything like this before ??

 

Any luck with this would be greatly appreciated. 
 

Edited March 6, 2023 by Oostenstein
Grammatical errors