Wind Vibration

[Hummer 06]

When I drive into and through a strong wind, I hear a loud vibration noise somewhere up front. At first I thought it was the wind deflector on the moon roof. Then a friend of mine jammed cardboard into a seam along the windshield and the noise seemed to stop. Has anyone else had this problem and how did you fix it? (Please don't say turn up the radio, because the noise is louder than that)