One problem related to clunking noise has been reported for the 2000 GMC Sierra. The most recently reported issues are listed below.
I purchased my vehicle used. The used car lot said all the clunking in the rear and vibration in the front was due to an aluminum drive shaft. I have been to numerous new auto dealers and no one can find the source. I have phoned gm and they say it is the first time they ever heard of clunking noise from the rear. Yet this problem is posted all over the internet. It may not cause a crash but it sure is irritating to hear over every little bump in the road.