Jeez folks, scare the crud out of the guy! :lol:
Matt check the small stuff first make sure all your lug nuts are properly torqued to 80lbs. Check your lug nut caps for being loose. If you find one or two on a wheel that are distorted and clacking around they can sound like long slow finger nails on a chalkbord, castanets, or or someone playing with plastic grocer's bag.
UJoints are something easy to inspect. If you have not greased them at each oil change they may be dried out. Now you usually feel a dry UJoint vibrating, as well as hearing a sqeak or squeal. since you are in tune with odd sounds your UJoints are not likely even close catastrophic failure point of launching upward, coming through the floor or Ripping your transfer case apart. Crawl under, give them a twist and see if they have excessive play or squeak. NAPA precision 344 has been the UJoint for every NAS LR product through end of P38s and DiscoIIs. They are half the price of OEM, built heavier and come with extended nipples for easier service.
Another possibility is corroded or loose brake mud shield rubbing.
Wheel bearings are an item that you would feel in the steering wheel as a growl vibration.
