I have an annoying squeaking noise coming from over in the airbag/passenger area too... It is slowly driving me nuts, and nothing is loose on the outside, so I don't know where it is coming from, so I really don't even know where to begin taking things apart... anyone else out there have squeaks or rattles and know how to fix them?
I have the same problem. Haven't had the time to fix it but have located the source (at least for my car). It is the A/C vent on the passenger side of the dash. Mine has gotten loose enough that I slipped a card behind it to stop the noise when I was coming back from BG. Shouldn't be too hard to remedy.
Late C-4s use what use to be the glovebox location for the air bag. There is no access into this area. Matter of fact, once the airbag is deployed, you have to replace the dash cap. Only thing you can do is to remove the lower panel and tighten up whats up there best you can. Also, a wild shot, but a lot of C-4s have ill-adjusted hood bumpers and result in the hood vibrating. This will result in sqeaking noise. Sometimes, this can easily be mistaken as coming from the dash. Check the round bumper next to the latches. Also spray armor all on the rubber trim surrounding the vent intake around twindshield wipers.