Comment 26 for bug 437429

I tryed "sudo -u gdm dbus-launch gconftool-2 --set /apps/gdm/simple-greeter/settings-manager-plugins/sound/active --type bool false"

but it didn't work for me.

"sudo -u gdm dbus-launch gconftool-2 --set /desktop/gnome/sound/event_sounds --type bool false"

work well and it relatively clean.