front end noise 4x4

[nvrsunk02]

4.0L auto 4x4 supercab 2002. Had a noise that sounded kind of like tire noise from the front end that increased in frequency with speed up to about 40 miles per hour, where it somewhat disapeared. Noticed yesterday though that if I throw it into 4 wheel hi, that the noise goes away on accelleration, and comes back when i let go of the gas. tells me its defintely something in the driveline. Any ideas? Hubs, gears, lube?

 

[nvrsunk02]

Realized that the gear lube i filled the diff up with was 80w-140. Could the fact that its not the recomended fluid be causing the vibe? I also noticed that the front driveshaft has a little bit of play, meaning i can grab it and it will shimmy a very little bit. Should this be solid? Not sure how to diagnose the hubs if that is the issue. What would happen if I ran the truck without the front driveshaft? Will it ruin anything, or throw anything out of balance to introduce new vibrations? I figure this is an easy way to see if the shaft balance or U joints are the culprit.