This tutorial shows how to turn off gnome login sound or adjust the volume when Ubuntu startup.

1.To turn off login sound,go to System->Preferences->Startup Applications.In Startup Programs tab scroll down to find out “GNOME Login Sound” and uncheck it.

login_sound1

In Ubuntu 10.04,go to System->Administration->Login Screen.There is an options says “Play login sound”,but this doesn’t work after I uncheck this option and I’ve no idea what this option exactly do.

login_sound

2.To adjust login sound volume.First,highlight “GNOME Login Sound” in first picture and click Edit,in command box change:
/usr/bin/canberra-gtk-play --id="desktop-login" --description="GNOME Login"
to
/usr/bin/canberra-gtk-play -V -40.0 --id="desktop-login" --description="GNOME Login"
Note,the -V parameter describes the volume in decibel (neg logarithm), so 0 corresponds to full volume and -50 can barely be heard.
login_sound2

Thanks clausfse from ubuntuforums