Final report. Used a black silicone adhesive. Put down a thin bead along tiny gap between rubber seal and top edge of windshield frame. Smoothed out with fingertip. Black car, black rubber and black silicone......impossible to see.....all blends. Let it set up for a day then a test drive.......no more whistle!! Problem solved. We had put up with it for the 3.5 months that we have owned, but the prior owner had listened to it for 8 years!!!