04 Avalanche Clunk

[mawint]

Hoping that somebody else has some input or experience with this but basically here are my symptons.

 

My truck is an 04 z71 and lately I have been getting a sporatic clunk at right around 55mph. It doesn't happen all the time and the intensity of the clunk is different each time I hear it. It seems to be coming from directly underneath if not a little bit forward of the drivers seat. Today I crawled under it and didn't notice anything lose but when I was poking around I spun the front drive shaft just to see if it had any play in it and it sounds like the transfer case is making a very small grinding noise, but could just be gears moving inside. U-Joints on both drive shafts were replaced last year with spicers. I can both hear it and feel it when driving. Anyone have any ideas on what else to check? Hoping to not have to replace the transfer case on this thing...

[spankrz]

you spun the shaft while the truck was on the ground?

[mawint]

The front drive shaft, yes, the back one has no play in it at all and does not spin.