Ok, I don't know if this applies to Cobalts, but I have a G5 coupe, so it might. When going in or out of driveways and parking lots at an angle, I have been getting a creaking noise. Like a suspension or trunk lid squeaking/creaking/popping.

Very hard to discribe, but it happens when the body flexes. Like going across a speed bump at a 45 degree angle. Anyway...

If you find that all of your suspension components are quiet, and tight, and the back seats arent doing it, HERE is what fixed mine.

It is too difficult to explain how it does it(on the internet), but take your tail light bulbs out, and coat the socket with dielectric grease where it mounts to the lens assembly. Don't ask how, just do It, and if you have a VERY elusive squeak/pop/creak, then this may very well be the fix you need. The pic is not a G5/Cobalt bulb, but if it WAS, grease where the black o-ring is.

 

Seriously? The bulbs were squeaking?

 

Sort of. The sound was a creaking and squeaking noise coming from the trunk/rear area. It was such a BITCH to track down. I used chassis ears, and a passenger in the trunk to find the noise.


Here is how it happens. Even though I'm not sure I can convey it well without ACTUALLY showing you.

When going over uneven surfaces, the body flexes. The grey, carpet-like material in the trunk isn't really attached to much, so it flexes DIFFERENTLY than the body itself.
This causes the carpet/cardboard to rub the tail light socket, causing it to "wiggle" in the tail light housing.
The rubber gasket on the socket, wiggling against the plastic housing causes a *fairly* loud squeak.
The open space of the trunk(mine is always empty) amplifies the sound into a LOUD squeak.
Fold the rear seats into the UP position, and it muffles and distorts the sound into a creaking and popping noise.

Its Just a REALLY weird fix that took me about 3 days to find. Figured I could save some people some hassle if it is happening to them.

 

weird..... ill check that out, i noticed the sounds a bit to.........

 

I was having the same issue, especially when its cold out. At first I thought it my spare coming lose.....

At least for the cobalt, I think it had something to do with the particle board cover in the trunk, but not something to with it hitting the rear light.