answer to clunk in the rear end

I couldn't find the post to submit this reply, but I hope this helps. While reading a Popular Mechanics magazine last night I found someone wrote in a question about a clunk in their Suburban that happens when accelerating from a complete stop. PM wrote that it's very common and probably from the splines on the transmission output shaft inside the tailcone. When you stop they bind up on the shaft's front yoke. "Compliance in the springs hanges the depth of the engagement of the splines." (most of us have the slip yoke). "When you reverse the direction of the torque on the driveshaft, the binding releases all at once, causing the clunk-which always seems to come from the differential."
"The cure is to pack the splines with a special grease that wont dissolve in the transmission lubricant." This will require removing the driveshaft to expose the splined area. PM says that fix is only good for a few thousand miles, and will need to be redone. You can also try a new front slip yoke to see if tighter tolerances will help.

The Chevy clunk is a well known problem. Never really seemed to hurt much, always thought myself, it was a combination of design and tolerances. Seemed to be worse, with worn transfer rear yoke bushings and rear ends with the factory limited slip.
When the 35 C starts clunking, I usually check the U joints, then the carrier bearings. Most 35C`s I´ve opened up, with more than 130,000 miles (or so) have had some carrier bearing play, from a little, to a lot. which sure enough causes a clunk.