I've learned I can't drive with my rear windows open because it generates this whopping noise that's so bad it hurts your ears and shakes the car a bit at highway speeds. Sounds like a helicopter sitting on top of the car. I'm thinking it's caused by the air waffling in the rear window/deck space, since it's only slightly better since I took off the rear seat headrests. It happens at speeds over about 25 mph, and is unbearable at speeds over 50. Does anyone else have this problem, or better yet have an explanation?