My 2011 SHO does it also, starting right at 72 mph no matter what the road surface. I was beginning to think it was something down inside the passenger side defroster vents (after beating on the passenger dash, airbag, and even slamming the glove box). I am on my second replacement windshield but it's been in place for over 3 years. And it only started this year when the temperatures went above 50 F. In the past two years, I've been fighting a cowl water leak that turns out to be due to the cowl seal no longer really sealing to the windshield. (Lost several cabin air filters thanks to the water coming in and soaking them.) Which leads me to wonder if there is another seal in the ventilation system that has lost its flexibility due to age and seasonal temperature cycles that could be vibrating at 72 mph rather than staying sealed. I welcome other thoughts!