This is a problem that has been around and not solved for many of us.
Please read posts below to get up to speed.
http://www.xoutpost.com/x5-e53-forum/...ght=wind+noise
http://www.xoutpost.com/x5-e53-forum/...ght=wind+noise
It was the seal in the upper trim piece of the windshield. The way I diagnosed it was to drive until noise occurred then push the upper part of the windshield near the mirror. When I did this the noise changed in pitch and almost stopped when I pushed hard. Found a glass shop that would remove the glass without breaking it, replace the trim and reseal it. The shop did a great job and told me there was little if any seal holding that trim piece in place. $180 and problem solved! Thanks to San Diego BMW for steering me in the right direction. I paid out of pocket since I did not want to pick up the dealer and drive him around at 75 mph to prove the point. I just wanted solved ASAP!