Please enter the following command, log out, and back in, and let me know if the problem still persists:
gconftool-2 -s -t bool /desktop/gnome/sound/event_sounds false
Please enter the following command, log out, and back in, and let me know if the problem still persists:
gconftool-2 -s -t bool /desktop/ gnome/sound/ event_sounds false