Mozilla just approved my latest update to the Better Gmail 2 Firefox extension, which now includes the ability to hide your unread Buzz count, and enable an audible notification when you receive new mail.
Thanks to Victor Zhang for creating the Hide Buzz Count script and Yansky for Gmail Sound Notify, and for giving me permission to include them in Better Gmail 2. Press play below to hear the new mail notification sound.
Better Gmail 2 [Mozilla Add-ons]