I had it bad, replaced the yoke to the upgraded 'nickel' plated one but still had it. It was loud as hell and intermittent but would do it loudest when reversing then driving forward at low speeds.
I can't say i found the cure but as soon as I swapped out the front shocks (stockers) it disappeared and hasn't returned.

 

Just out of curiosity, when you guys are having this "clunk", are you experiancing it on trucks with Step Bars on them? The reason I ask this, is because we have seen hundreds of cases and so many in fact that GM has a Tech Bulletin on Aftermarket Step Bars causing mysterious "clunk" sound resonating through the vehicle.

Or...is this "clunk" only heard when shifting from park to drive or reverse? If you guys will give me some detailed info, I'll try to help you out as best as I can.

 

On my Z71, the clunk came from the overload spring making contact with the spring pack. Putting it into reverse / drive would cause the diff to rotate just enough to force the overload spring to rub the spring above it. The GM fix was to put a set of rubber sleeves over the ends of the overload springs. Fixed it for me.

 

My HD was clunking when I bought it (used, April '08). Pulled the driveshaft out and smeared it and the tranny splines with Green Grease and it hasn't made a noise since. Tractor Supply and Academy usually have it, it's waterproof, high temp, lasts long time.

 

Mine was taking off from a stop light, and sometimes when slowing down coming up to one, but not as much. didnt do it all the time either..

 

my cousin had this clunk...turns out it was his pittman arm, just wear and tear

 

I had a clunk just as leaving stops that began after a routine rear diff service. Turned out that the tech used 75w-140 synthetic and thought it would be okay. Drained it, and switched back to 75w-90, and no more problems. Seems the thicker lube was causing the Gov-Loc to stick.

 

It's obvious that from the numerous "clunk" comlaints, and fixes to the problem that not everyone has the same clunk. The "clunk" most commonly heard through the typical situation is either the Slip Yoke clunking or the Rear Spring clunking.

Like afore mentioned by BigTex, the GM fix if the urethane inserts to stop the sound from the springs. Now, however GM has a reccomended fix for the slip yoke by replacing it with the Nickel Plated yoke, tghis does not mean that it will work for the othert clunking complaints. I've replaced the Nickel Yoke many, many times ans some indeed come back witht he same problem and it seems the yoke didn't fix it. That's not to say that it's always the yoke making the noise, as you can replace the yoke and then a few weeks later, the clunking comes back and it can end up being a totally different culprit altogether.

Most commonyl the clunking culprit is a steering shaft, slip yoke, rear springs or aftermarket step bars. The step bars mount diffrently and they cause a popping or clunking because of binding on the mounts.