So it sounds like plastic crunching when the car twists? And you indicate "hard top" (vs. "soft") above - there have been several prior posts about the attachment hardware for the rear of the hard top... see for example:
Bough a used hardtop. Squeeked like hell. Lubricated all the rubbers. Still squeeked like hell. Adjusted the complete system and made it more loose / float on the car. Now it is perfect.
Dig into some www.ppbb.com archives for hardtop adjustments...