I have a 99 classic and a noise has developed from the drivetrain (i think) it starts around 40 mph and sounds like tire noise or a type of howl. Increases and decreases with speed. It's pretty loud.s So far we have gone through the rear end new axle bearings and pinion bearing. Next completely re-built transfer case, bearing seals, gears all good. I'm assuming the tranny is good , an aw-4 ,just seviced, no noises shifts great but it's an assumtion. I actually went and bought new tires to rule them out, and we checked the u-joints they seemed good but have 100k on them. could this be a possibility? I'm kind of running out of guesses. Any thoughts thanks alot.

 

Wheel bearings?

 

Actually we had it on a lift and there was absolutely no play on any of the tires, and no play in any thing on the front end.