Car Stereos: Speaker problem., rattling sound, resonant frequency

Question
I just bought a used 2003 Mazda6 with stock bose speakers. I notice that I
will get a rattling sound the higher I turn my speakers up and possibly the
faster I go. It almost sounds as if you were to put a bead in tupperware and
shake it around.It is not a constant sound though, very random in timing and
length. It seems to kick in during higher pitches so I don't think it is my bass.
I could be wrong though. I was wondering if there is any way to easily fix this
or if you suggest some troubleshooting before I take it in somewhere.

Answer
Hi Nate,

The issue is probably something of loose trim somewhere in the car, or near the speaker.  It doesn't necessarily have to be bass that does it, as higher frequencies just might hit the resonant frequency of whatever it is that's loose or broken.

If you're up to it, you can try and pinpoint at least the general area of the sound.  Just start pinning things down with your fingers to see if you can eliminate it.  Start from there, and soundproof anything you might find.  If it's behind a door panel, and you are comfortable with it, remove the door panel and look for loose plastic, broken pieces, or things that could've fallen into the door.

Good luck,
Justin