did you try putting the top back on
Seriously though try checking the windshield for leaks. I had a really bad wind noise in my work car and was able to isolate it to the seal around the windshield.
The easiest way for me to find out, is to go for a drive with a buddy and have him move his fingers around the edge of the windshield while you hear the noise. Either he will feel the air or the noise will change when he gets close.
Give it a try, or take it to your local windshield place they may have a ultrasonic divice that could do the same. Not sure if those work on convertibles though.
Good luck