Hey guys gm has a bulletin on this. It is the intermediate drive shaft. All that needs to happen is to get the lube kit and lube it. It is happening on my 04 silverado. I went to the dealership and paid $15 bucks for it and the instructions were included. It does not look that hard but just time consuming. Nothing is broken it is just a poor design and has to be lubed.
This post is for those guys like me that are out of warrenty. Otherwise if you are in warrenty take it in.
2004 EXC Silverado 6.2L
Mods:
6.2L L92, Ported and Polished stage 3 heads, 95mm Throttle Body, 100mm MAF, NA, Pacesetter LT Headers, Magnaflow X-Pipe Muffler, Electric Fans, 160* thermostat, 2" Drop Shackles, Hellwig Sway Bars Front and Rear, Monroe Reflex Shocks, NGK Spark Plugs, AMW Oil Catch Can, 17"x10" wheels on Kuhmo Tires.