I have "fixed" this. The sound in question can be turned off under Login Window Preferences > Accessibility > Sounds > Login Screen Ready.
I realise now that this is because these sounds are system-wide and not a user preference. This is *not*, however, an intuitive place to find the setting. Could a "System Sounds" link of some kind be placed in the Preferences > Sounds Menu? -- gnome-sound-properties: No list-box for when one gets to the username/password screen https://launchpad.net/bugs/39128 -- desktop-bugs mailing list desktop-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/desktop-bugs
