Many times I have felt the sound clip played while login to Ubuntu desktop is unwarranted. I am not interested in this login sound, which makes my kids to come to me and start doing all possible things to prevent me from working. My Ubuntu version is 10.04.
The following command plays the login sound while a user login.
/usr/bin/canberra-gtk-play –id=”desktop-login” –description=”GNOME Login”
This command is invoked by Startup Applications. So to disable this login sound navigate to Ubuntu main menu -> System -> Preferences -> Startup Applications -> Startup Programs and remove the check box in GNOME Login Sound.
The following screenshot shows this.

