ram_g,
Answer to your question - that metal speed nut doesn?t belong there.
As for the buzzing noise, could be many things including the radio itself vibrating. I have been chasing various squeaks and rattles in C4s (84 Z51, 91 ZR-1 and 94 ZR-1) since March 1984. Been successful at times. Currently, I am chasing what sounds like a cricket in front of me either inside the dash or the engine bay.
What Corvette 95 is describing is a metal clip that attaches to the back of radio bezel towards the driver side. If you are missing that piece, let me know. I?ll mail you one.
https://images.factoryoemparts.com/m...8767819-4.jpeg