[rboatwright]

After talking about this with some others, the noise shows up on other chevy cars and pontiacs. There is a thought that it could be coming from the internal air filter. His car does it at ~75 mph, my van does it at ~65 mph with a high crosswind. We are thinking that the air is getting forced into the filter too hard and causing a kazoo effect on the filter. I am going to try removing the interior filter next time I hear this happen. I have not yet taken it to the dealer since its very hard to re-produce. If there is not a crosswind, it doesnt do it.