I have a theory that I haven't tested but figured I'd put it out there. I know the cause of the noise is because the hvac system lets too much air into the cab. There is a door deep in the top passenger side of the dash that opens to let the hvac system either heat or cool that air, when recirculation is on that door is shut and the hvac system is using air from inside the cab. My theory is that the door up in the dash is letting too much air into the cab and it can't get out of the cab fast enough at higher speeds, so essentially its preasurizing the cab and some of the air is getting out through the front door seals or somewhere around there.
WHAT TO TEST-
When you hear the noise crack the rear sliding glass window maybe half an inch and see what happens. I wouldn't use the side windows because that will cause too much noise. If you have a sunroof you could try venting that as well.
I could be totally wrong but worth a try I guess.