I have the same issue with my 540i and my front windscreen. At around 80mph I can hear the air whistle through it.
I took it while under BMW warranty to Stevens Creek BMW who promptly advised me it was because the glass had been previously removed by a non authorized BMW dealer and subsequently would not be covered by the warranty. I couldnt believe this absolute BS. How they could tell this from just looking at it even though everything still has the original BMW part numbers amazed me.
But its not surprising since this is the same company who charged me for repairs last November and then subsequently recharged me again for the exact same repairs in May.