Do you have a sunroof? I had that whistling sound over 80 km/hr. Turns out I had some pine needles in the seal for the sun roof. I vacuumed around the seal and took it to a touch less carwash. Haven't had the whistle again...knock on wood
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Love 911's
Previous cars: '99 GTi, '01 Subaru TS, '06 Subaru RS, '10 WRX, '11 WRX STi, 2016 m235i