I've noticed that on occassion, that one of my rear doors will wistle at high speed like around 140mph (j/k). Actually, I've got it figured out. Some of my passengers like the window open and do not close their window all the way when they leave. If the window is up in the seal but not all the way in, its hard to see. All I do is open the windows and then close them all again and the noise goes away!

Hopefully your noise is this easy!