The "Sound Preferences" panel is for editing the sounds played for the current individual user; the login sound affects all users, so you'll find it under the Administration menu's Login Window panel, under Accessibility.
Does this answer meet your needs? If so, please close out this bug to Rejected state. tjeu: your problem sounds very much like bug 52649. In the future, please do not submit new bug reports in the comments of other, unrelated bug reports. ** Changed in: Ubuntu Status: Unconfirmed => Needs Info -- login sound cannot be disabled https://launchpad.net/bugs/49382 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs