Try installing targa top anti squeak pads
http://www.mamotorworks.com/corvette...1-163-762.html
These Seal Pads are OE for 1992-96 Corvettes. Plant engineers added them to the roof panels to quiet some of the continuous squeaks and rattles. We've expanded the idea by using a sound insulation material. Retro your 1984-91 or replace existing foam seal pads on your 1992-96 Corvette. Adhesive-backed for easy installation. Instructions included. Set of 4.