Have you tried removing the bulb to to see if it still buzzes? If the thing that's buzzing is something directly touching the bulb -- which I guess would be the socket -- then maybe you just don't have a tight fit in there.

I'd look for some electrical tape rated for high temperatures (such as 3M Polyimide tape) and wrap it once around the bulb threads -- not the entire thread area, but just the part closest to the glass. Then put the bulb back in as see it if still buzzes.