In maverick, I get the login sound when my computer starts up and I auto-login.
The happens despite the fact that I've turned off the "play login sound" on the administration > login screen dialog.
How can I turn off the login sound playing?
The login screen dialog dictates what happens when GDM (The login screen loads) The sound you're likely referring to is actually the GNOME Login Sound which can be disabled in the Startup Applications windows under
System > Preferences > Startup Applications
Maybe try Preferences > Startup Applications > Gnome Login Sound, and disabling it.
EDIT: I would also like to add that you change the sound to your whim: you could put any 10-second sound when Ubuntu starts up.