07 2500HD Rear end thunk

[KShortell]

The splines on the slip yoke at the transmission and/or transfer case will do this on occasion, particularly after a hard stop. This is more of an issue on trucks with longer or two-piece driveshafts and has been since at least the 70s. There is a special, thick grease that GM uses to quiet it down. It is blue and often referred to as "Smurf" lube or something like that.

I've been fortunate that my '08 Silverado doesn't really do this. My old '86 Suburban sometimes would.

Good luck!