Well show you how to disable both login sounds for good.
Lets disable that program!
punch System > Preferences > Startup Applications.
Scroll through the list and find the GNOME Login Sound program.
Uncheck the checkbox (or click Remove to permanently remove the option from this list).
To disable this, select System > Administration > Login Screen.
Once unlocked, you’re able to uncheck the Play login sound checkbox.
If you want to turn them off, check that you disable both of the login sounds!
