1997 Jeep Grand Cherokee

I recently used part time drive to get out from a slippery mud. I pull lever again to 2WD and it didnt work. I then drove about 500 meters on paved road and finally drove with ease on steering as it disengaged by itself. However from then on I could hear humming sound like something is rolling forcefully if not touched against rubberized surface. Like a bearing started to worn down.
I lift the front end up and checked tire rotations. The tires do rotate but with some effort. I noticed the axle also rotate with the tires but has no power to move the vehicle when stands down.
What I want to know is whether the axle and tires rotate simultaneously when only the 2 rear tires are engaged. If this is common, and if not, how can I get to disengage the front wheels completely.
What can I do to stop this sound. I guess its from the axle. (Universal joints are perfectly functioning.
August 6, 2013.

Check out the related content below while we wait for the question to be answered by a professional mechanic.