Yes, it could be a transfercase issue. I was thinking more along the lines of the problem being in the rear differential. Noises will travel along the drivetrain and are difficult to pinpoint exactly where they originate. Can you get this truck on a lift (or up on 4 Jackstands) and try to recreate the noise?
What is your axle code? Its on a sticker on the drivers door. The point I am getting at with that question is, the limited slip differentials make some weird noises, shuddering, moaning/groaning type things when the clutches go bad. I wouldn't exactly say that the noise generated would be a "banging" noise though.
Have you been inside the rear differential recently? (you said in the first post that you had replaced the front and rear wheel bearings, that would indicate that you have)
When you opened up the rear differential to remove the axles to facilitate the bearing replacement, did you replace the cross-pin keeper bolt? Those are notoriously weak and break, that condition would cause some strange noises as well since it would allow irregular movement of the spider gears.
GO PATRIOTS!
