Sporatic clunk on 04 Avalanche.

[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 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, I haven't checked the fluids yet, didn't have any tools with me or fluid to do it. 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...

[00Beast]

First thing to do would be remove the rear drive shaft and grease the splines on the shaft inside and out. That's a common problem on the newer trucks.

[mawint]

I have had the driveline clunk noise ever since I got the truck, even after they greased splines when they installed new U-Joints. I also have the G80 locking rear end and have grown accustomed to noises from both of these systems. From the best way I can describe the noise is that it sounds like something is hitting a wheel every so often with a piece of something metal and it clunks but the weird thing is, is that it sounds and feels like it is coming from somewhere near the drivers seat.