most likely, the axle isn't connected to the engine through the diff. which is what holds the truck when its not running, it'll be the same as a Rwd because thats what it essentially is.
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Yes.

The tires don't disconnect from the axles (no auto or manual hubs, no Center axle disconnect, etc) so they're always spinning, which in turn spins the front driveshaft. The transfer case side of the driveshaft is not connected to the rest of the drivetrain while in 2wd though, so no worries about bind. That's why there's no real difference in fuel economy between the 4wd and the AWD versions.

 

Had truck serviced at dealership. They replaced front hubs and bearings both sides $643. Sound is gone!! In my original post I called the sound to be a thunk/whine. It was better described as a growl sound that started around 15 mph and got louder the faster I went.

Thank you all for your help!!!!

 

Hmm i just replaced my front drivers side axle a few days ago, now it started making the noises like you described, it would clunk going into gear then growl and got louder. I didnt notice any play in the bearings, and im quite sure the cv assembly is in correctly, so im assuming its the diff or the end of the dv that goes into the diff. Damn i hate this truck, so many problems in such a short amount of time.