I have noticed a small systematic squeeking noise behind me while driving slowly on my dirt road. The sound is behind me and very much resembles the sound your trunk would make if it was left open slightly while driving. The sound is quiet, I can almost nothear it if the AC is on. I can only hear it while driving slowly (around 10mph) on my dirt road. I have never heard it while driving on a main road. It is as if something is loose and wobbling up amd down when I drive.

What could be causing this? Does anyone have any ideas or amything similar? I actually got out of my car in the middle of my street this morning to make sure the trunk was not ajar when leaving for work.

Thanks for any advice and thanks for all the help you guys have given so far. It seems drivernumber3 always has exactly what I'm looking for

 

Could be the seat, or the seat belt. Can you mimic the sound if you have someone press down on the trunk while it's parked?

 

Not sure if this is the sound you are hearing, but I would hear a squeaking noise from the rear whenever I went over a bump, even slowly. I swapped out all the struts and could still hear it. As you said it sounds like the trunk is left open,

If you go to the trunk, try pushing it down. If the trunk can still move down a bit when closed then unscrew the adjustment screws until the trunk no longer moves down when pushed on.
What I think was happening, in my car at least, was that little bit of play allowed the trunk to move up and down slightly when I hit bumps. By adjusting the screws there is no longer any play in the trunk and the squeaking has since stopped

 

I tried pushing down on the back of the vehicle to attempt to recreate the noise, but heard nothing. The noise seems too distant to be the seats or seatbelts.

I will look into the trunk like Jason said to soon

 

Could be bushings on rear trailing and/or lateral arms. I know my UMI trailing arms with poly bushings have grease fittings to put a little grease in now and then to stop squeaks.

 

believe it or not I had a similar squeaking sound that was annoying as can be It took me awhile but i found that one of the brake lines on the drivers side in the engine bay was rubbing on the trans housing underneath the master cylinder so i pushed it back a bit and it was glorious no more noise