yeah, i had that a few months ago. and its back now.
originally mine went due to a bad ujoint i failed to replace soon enough. (it literally fell apart right after i pulled it in the garage to fix)
kept getting worse and worse till it would do it at lower speeds as well. and would growl when slowing down.
its doing it again now after being fixed and will be fixed free of charge.
not saying thats what yours is, but sounds very similiar to my situation. this is a video i took to help hear where it was coming from.
in cab it sounds like its coming from everywhere. but this video shows its coming from the rear.
sounds a little funky due to shitty gopro lol.
if ya got a camera that can be mounted various places it will help you find where exactly its coming from also. i had two cameras, front and rear. front was queit so rear it was. i realize not everyone has gopros sitting around, but you can also have someone lay in the bed, with their ears close to over the axle and see what they hear. sound in vehicles is funky, it can travel along the frame and make it sound like its coming from somewhere else.