[MattBianco]

I am not an engineer but I play one at home ....at least being honest about it.

My guess is the more aerodynamic a shape is, the higher and more consistent the air pressure against its surface, and the less aerodynamic, the more likely you will have lower pressure against the surface (except first areas of contact) and areas of very hight and low pressures on its surface. It could well be the shape is well designed -when windows and roof are closed- but any opening, would cause the high pressure against the surface to be breached, funneling air in, and producing all kinds of sounds.

My poor kids have learned that as soon as we are over 35 mph, they have to roll up at least 3/4 up.