I know someone else has to have this - I had it with my '95 Z28 - and now I have it with my '96 Convertible Z28. The only way to describle the noise coming from the dash is a buzz or a very high frequency rattle. It is related to RPM (resonance, obviously). It's not loud, and it sure does not sound critical by any means - but boy is it annoying! Anybody have this - or better yet successfully address it?

 

Mine started to do that this summer too. Sounds like it is the plastic upper dash cover rattling. It sure is annoying. I haven't got around to looking at it much but I will over the winter.