Time for an inspection. Sorry I can't be better help over a computer, but this should be checked by someone who can see it and tug on various parts. Blazers are known for two common problems but I'm pretty sure they both only apply to the 4wd versions. One is ball joints. These vehicles eat them for lunch and replacements are needed every 50,000 to 80,000 miles. The thing is though they won't usually make just one single clunk, ... Usually. That's why they should be checked.
The second thing is the rubber mounts for the cross member that the torsion bars are attached to under the seats. Usually they will rattle over bumps but they have been know to make one clunk when you start out. This won't apply if you have coil springs on front.
Please consider a to help us answer more questions.
Wednesday, January 19th, 2011 AT 7:57 PM