Update....After a couple weeks of top down weather I almost forgot I had a whistle. Then a week of rain, before I could get back to trouble shooting. I used blue painters tape where glass meets windshield frame on all fours sides. Then also taped along top edge of windshield frame where it meets rubber. Took a quick run down the highway and.......no whistle!! Hot Damn! I then started removing tape and driving and finally isolated the whistle within an 8-10 inch stretch centered above the rearview mirror at top of windshield frame where it meets the rubber that mates up to the leading edge of the top. Now I'll take a closer look at that rubber during daylight to see what needs to be done. The previous owner said they listened to that whistle since the car was new. Dealer never could figure it out. Looks like I'm close now.