Shoutbox Sound : Sound on new 'Shout', 'New shout' & 'Delete'. Checkbox option for sound on or off OR a volume slider.
YOU NEED TO DO SOME WORK!
Here goes: You need to find somewhere to host two files or somewhere that will allow you to hotlink to them. This plugin will work for modern browsers only. IE9+, FF, Chrome + others that support HTML5. For older browsers that do not support HTML5 sound, the button will not appear.
If I've lost you already then here are some more instructions and advice.
Host: It's hard work finding a free host that will accept mp3, wav and ogg files. After some searching myself I found Fileden.com( no idea about this one now ) & Dropbox.com ( I believe new accounts need to pay for the public folder ) If you can use photobucket then you can use FileDen, they work in the same way (ish). Sign up for an account (I had no problems with spam etc) From your computer upload your sounds and then use the DIRECT link to the file to use in this code. I'm sure there are many other file hosting sites.