If it's only happening in 4wd AND when you're turning hard, then it's very likely that the front end is just binding a bit. Every 4x4 truck I've been in does this, including my 07 2500.
But, if it's happening in 4wd WITHOUT turning hard, it'll likely be either your left or right front uJoint. You might be able to hear it in 2WD as well. My lefty went out and it was only when my front end started sounding like a hydraulic impact driver in 2wd did I realize it.
And if it's happening when you're shifting, it could be the uJoint or CV joint on the front drive shaft. Since that's a driver side drop on 3rd gens (and most trucks in general), the sound will be biased from the driver side.
It's really easy to test for a bad uJoint. In 2wd just hit the parking brake, go under the truck, and play with the front drive shaft. Listen for clunking as you try to rotate it for clunking, that'll likely be either the left or right. Then try to move it up and down and side to side if the L & Rs are good. If you get it moving in a way it's not supposed to at the joint, then that's the joint that needs replaced.
Some additional things for left/right uJoints:
If it is a left or right, figure on replacing both. Also check the front wheel hubs for play. You're going to have to pull them off to get to those uJoints anyways, so replacing them if they need it now just saves time.
If you plan on doing it yourself, have a small hydraulic hand press to press in and out the joints. They're gonna be crusty and not want to go anywhere.
If you get greasable uJoints, GREASE them. They'll outlive their non greasable counterparts if you do, and die prematurely if you don't.
Put the truck in 4wd when you start to do the work, or make sure the mechanic does. There are some components in the axle that will shift if you pull the axle shaft in 2wd.
If your brake pads are getting thin, now's the time to replace them.
