I think it's the automatic climate control vent doors. I can hear one make an odd vibrating noise when it actuates, and it's almost the right frequency. Of course I'd prefer not to have to disassemble the entire dash.

Anyone have a similar issue and a fix that's just not obvious? I've been as far up inside the dash as I could get from underneath and from the center console while installing my stereo...the only thing I found was a cable connection that had come out of a bulkhead mount, and it wasn't in a position to make any noise anyway.
If not...how hard is it really to get to the doors? I'm capable of pulling everything apart, I'd just rather not spend an afternoon doing it.