It's like blowing over a bottle and making a noise, or like in a flute...only, you are in the bottle or flute. The wind rushing over the top of the sunroof vibrates the air inside the car, and when all of the right conditions are met, it reverberates (like in an accoustic guitar) and makes a lot of noise.

Maybe this isn't exactly-technically-100% correct, but it is the general idea.

 

Love the sunroof, safety feature doesn't bother me at all... But one could say I'm not "used to it yet," because this is the first time my tC's seen warm weather... :p

 

yeah, no kidding. I never had a car with a sunroof. Now I'll never buy another one without it.