Ok, so just got back from a weeklong trip, and took the mustang out again.
Had the window rolled down, and noticed a strange sound every few seconds
(in every gear, at fast and slow speeds).

It sounds like its coming from inside the drivers side wheel well, behind
the tire, almost like a quick half-second hiss of high pressure air
releasing, or maybe a thin tree branch.

Its definately not every wheel rotation, or at gear shifts, so I'm
scratching my head. Computer reads clean, I just scanned it. <1k miles on
it, so cant need oil yet.

Going to the dealer this weekend, but if anyone knows what it is, im all
ears...