Bass creating unwanted noise(gas cap)

[SpaceGoat]

When i have my subwoofers kicking it makes my gas cap cover vibrates like no other. It makes annoying noises (not that i can hear in inside but outside). Has anyone "cushioned" it with anything, if so what? Thanks

 

[Tuna]

I got some felt pads from the hardware section of WalMart and stuck them under the lid to stop some of the noise that my lid made. Then I ordered new springs to hold the door down better. That seems to minimize the amount of vibrating and bouncing that the lid was doing. If I remember correctly, Ecklers had the springs.
They can be a pain to install however.