OK, so here is what happens:

If I am driving with the windows down at more than 40 MPH than the tweeter in the right front passenger door makes all sorts of noise. I should clarify that its not rattling, its some kind of feedback coming from the tweeter.

The noise stops when I:

A) slow down below 40 MPH or
B) roll up the right front passenger window.

The noise is not related to the volume of the stereo or it even being on. I have an aftermarket head unit and I have tried turning it off and even taking the face plate off and the noise persists. As long as I am driving 40 MPH+ with the front passenger window open (any amount, not just all the way) I get the noise.

I have an aftermarket head unit installed but the speakers in the doors are all factory. This just started out of the blue yesterday.

Has anyone experienced something similar or have some ideas? The local dealer's service dept. is booked through mid-May so if its something easy, I could probably fix it myself.