I have the same noise problem with my 2020 1500 Duramax 4WD. Took it to the dealer they said they can't find anything wrong. Took it back and had the service manager drive it. He said it is "bed shift". They tightened the four bolts
holding the bed to the frame. He said there is no fix for it. Problem is still there. Truck is still under warranty. Has anyone heard of Bed Shift? I think it's BS.