clunking from rear when I put vehicle in 4wd

[rsekrecre1]

I have a 2001 GMX Yukon Xl and when I push on the 4wd it engages the light comes on then I move and after a few feet, the truck makes clunking noice that sounds like it is coming from rear end area. Like the hubs are not engaging. Any help.

 

[RenegadeTahoe]

I have a 2001 GMX Yukon Xl and when I push on the 4wd it engages the light comes on then I move and after a few feet, the truck makes clunking noice that sounds like it is coming from rear end area. Like the hubs are not engaging. Any help.

The sound may be coming from the transfer case... or driveshaft the rear-end doesn't actually have locking hubs, they are "locked" all the time... not meaning it has full-time lockers, but the rear-end is not like the front-end... the hubs don't lock. I'd consider having someone help you look for where the sound is coming from. It could be your U-joints... do you notice it when you put it in drive?