Ok, It's gotten worse and more annoying. I'm cruising at 25-30mph or less(may do it at higher speeds but road noise cancels everything out) and I hear this whirring sound. Imagine one of the little tops with the rip cord, it sounds like that. It's not consistent, more like a wave, there's highs and lows to the loudness.
I've shut the engine off and cruised in neutral to rule out the engine.
It also reverberates through the floor of the truck. It's hard to pin point the sound, sounds like it's from under the truck.
I'm guessing the pillow bearing for the drive shaft or a bearing in the output of the trans or similar.
The wheel bearings are all brand new, the transmission was replaced back in like 2002ish, I have paper work with the date, but anyway.