A simple method to block the sounds from the Lil XT
pet Blizzard recently released WITHOUT shutting off
sound entirely.

To Use: Unpack the Sound folder into your WoW Data
folder (NOT Interface\Addons). It will be in the main
WoW folder. Then restart WoW. You shouldn't hear Lil XT
anymore.

Down side: You probably won't be able to hear the XT in
Ulduar either, but if you REALLY want to hear him, just
remove that Sound folder again.

Note: Empty sound file shamelessly borrowed from
TrainWreck.