I'm using a few 'normal' Firefox Addins but I am using Vimperator which to me seems like the most likely suspect.
What kind of noise? Not the Internet Explorer "click" is it?– outsideblastsFeb 11, 2010 at 6:37
If it is the Vimperator beep, you can try disabling it by putting the following file in your .vimperatorrc file:
Disable the plugin, restart firefox, and see if it still happens.