Shaky Headlight

Is there anyway to tighten the Headlight housing on a 91 Vette? when I drive with the Headlights on ,on a semi rough road, I can see the right Headlight bumping up and down a little and the left one stays as solid as can be. It's not that major, but would like to fix it.

Thanks

I have a 91 also and have the same problem!