I appreciate your line of thought, but how will this pass any speed while driving (being cardboard)? The noise doesn't appear until 45 mph is reached. Good thought, I just don't think it will hold up at speed. Or maybe this, a thought that just came to while while typing. Use that same piece of cardboard and tape it over the front of the sunroof glass to see if a deflector would work. Or instead of that, just try some duct tape over various parts of the glass (just the front, just one side then the other, just the back...) to see if the leakage is taken car of. Just do parts of the glass to eliminate parts of the noise...keep thinking.When you say sounds like a window slightly 'cracked' open, are you talking like an inch or two, or ex: 1/10 inch. I'd think a seal issue would be like the latter and sound like a 'hiss' or 'whistle'. If it's more a low-frequency 'buffeting' sound could be aero. maybe the factory does a better job acoustically isolating the glass. Kind of a goofy idea, but maybe you could fabricate a test deflector (strip of thick cardboard with folded legs/supports at each end, tape) just to see if it makes any noticeable difference.
