4x4 Problem. Help!
 

I have a 2005 F150 with the 5.4 liter. I needed the 4 wheel drive the other day after I bogged the back tires down. When I put it in either 4 low or 4 high I can feel the transfer case lock in but all I got was a clicking type sound from the front end with no pulling. The next day I locked it in on dry pavement on a hill the truck would normally not pull itself up in idle, but after I locked it in, it idled right up the hill no problem. I've had it off road since then and got Nothing but the clicking noise again. Sorry if this is confusing. Any ideas on What the problem might be?

Lock into 4x4 and out, a bunch /on gravel.

What will that do? And do it while driving or What?

It only makes the grinding/clicking noise when in drive, doesn't do this in reverse. Could it be a bad IWE? I'm assuming that's what I've always called a hub. Any help Would be greatly appreciated!