Wind noise/whistling when A/C on

[pyoung62]

OK, I tried searching for this, and I found a lot of posts on the mirror whistling issue and even a couple references to AC whistling, but nothing real useful. Here's what I have going on with my '08 135i coupe. When the AC is on and recirculate is off, I start getting a wind noise/whistling at about 50mph. By the time I get to 75, it's pretty obnoxious. If I either switch it to recirculate OR turn off the AC, it immediately stops. It's only there when the AC is on and not in recirculate. I found one person who reported something similar and said his dealer found a loose cowl below the windshield, but I checked mine and it's all good. It's not my mirrors and my windshield has not been replaced. Anyone else have this going on? I really don't trust taking it to a dealer when it's this open ended and I have no other clues as to the cause. I searched the TSB database and didn't see anything there either.