Vibration Noise

[blue99]

Purchased 2005 4.4 X5 with the Performance, Activity and Premium packages (now 6 wks old). Under certain conditions, a high pitched squeal/vibration noise develops which seems to originate from behind the rearview mirror mount where it attaches to the windshield. Only occurs at speeds greater than 65 mph, usually when there is a head or cross wind present. This is not a small noise....can't even drown it out with the mega-watt stereo. The dullard that I am is convinced that it the culprit is some sort of harmonic developing under those conditions. Of course the dealer has twice failed to recreate (and to fix) this particular malady when it has been brought in for repair, and there is now a lot of head-scratching coupled with sideways glances of disbelief by the techs as I attempt to press the issue. Does anyone have ideas/knowledge that might help?