I know this thread is a little old but just Btw to mention it, while I still haven't found any smoking gun for this, for some reason now that it has been steadily colder, the noise has almost completely gone away.

For sure it is still there but I really have to hit some good hard bumps and in just the right way, and with all the major traveling I have been doing this past week for all my Christmas shopping and gatherings, I would say its about 85% less then it has been in a long time.

Funny.

 

Mine also does this, i have a 2000 LS with 109k. Now i havent looked under it, but yea everytime i hit a bump it makes a clunk in the rear.

 

Mine is a 98 with 125,000 miles and has recently started doing the same thing.

 

dried out rubber bushings? i have a 98 zr2 90k have a sound similar to yours and i noticed the bushings have shrunken. maybe that is it?

 

Ressurecting this old thread....same noise out of my '04 Blazer, same location (WBFair's descriptions were spot-on...could not have described it better myself!). Seemed to come from the area where the spare tire carrier hinges mount to the body. Even had the wife drive me around while I sat in the back and listened to it. Could never replicate the sound - had to be driving around town on rough streets.

This morning I pulled off the spare tire and threw it in the cargo area, and the noise has gone away. So it's evidently related to the weight of the spare tire on the carrier. Not sure why, since there's no evidence of play in any part of the carrier, but will try to get it apart this weekend and see what I can see.....stay tuned.

 

So I did a little investigating the past couple weeks. Here's a diagram of how this contraption is mounted:




One common source of noise is the bushings on the hinge (#11 & #26), as well as the hinge pins (#10). As these wear over time, the hinge can develop play and start rattling. On my Blazer, I didn't have much play - not enough to make noise, anyway.


For me, the problem was in the upper mounting bracket located between the inner and outer body panels. This is #6 in the diagram. This bracket, as well as the lower one (#7), appear to be spot-welded to the body. The carrier bolts (#14) screw into what are basically square nuts (M10x1.50) welded to the brackets.


So here's what I think my problem was:





It's hard to see, but the bolt hole on the right appeared to be pushed in slightly. When I screwed the carrier bolts into the holes, this was the only one that I could get to move a little, when I grabbed hold of the bolts and tried to wiggle them around in the holes. Probably not unusual for the forward-part of the brackets to get a little out of shape, since that's where most of the stress is going to end up if your carrier swings out all the way to the stops. Thanks to my secondary latch, this has never happened while driving, but there's been a time or two when I was parked on a slope and I let the door swing all the way out on its own.


On the inside, neither of the brackets are very easy to see, and the upper bolt holes were completely blocked by the inner body....until Mr. Bi-Metal Hole Saw showed up:





This gave me a better view of the bracket where the bolt hole was pushed in a bit. Two things stood out: 1) the end of the carrier bolt was almost touching the inner body; and 2) the bracket wasn't completely seated against the outer body - there was about a 1/16" gap around that end of the bracket. I took a nylon washer and shoved it in the gap, to see if it was the gap causing the noise as the body panels flexed.





(I put tape over the edge of the bracket to keep the washer from possibly falling out)


After I did this, I've got no noise from the spare tire carrier. Sometime when I have access to a welder, I'll put a few tacks around the bracket and (hopefully) fix it permanently.

 

Well I'm glad I can shed some light on this. I have fixed a lot of these types of noises at my shop. There are a couple culprits I usually find. First, check the rear window lift glass (if you have an older model). If it's not tight to the tailgate, it will rattle and pop. Second, (also for older models with glass and tailgate separate), the rear latches and strikers for the tailgate get worn, and will rattle like a snake. Some electrical tape around the pin or a cloth put over the strikers and closing the tailgate (jamming the cloth in it) and going for a quick drive will tell you if that is your problem. Another problem is backyarders, and bad mechanics. Too many times I have pulled off the interior trim in the rear to find the snap clips that hold it to the body completely broken off and rattling around inside of the trim. There is no fix for this but replace the trim, and that is no small task, and it is not easy on the wallet. Third, loose spare tires. Get underneath (non zr2) and give it a punt. If it moves, tighten it. For zr2's, the bushings and the mount for the spare tire tailgate rack can cause infinite problems. From bushings, broken welds, loose bolts, you name it. This is usually the issue, and even more so if it has ever been removed. NEVER USE AN IMPACT ON IT. EVER. This can ruin the mounting holes, or over tighten and crush the body. Take your time and do it right. Hard labor can make a man out of anyone. Good luck guys.