If you think that the Ubuntu Login sound is really annoying, especially when you forgot to turn down the sound the day before shutting down the computer, here is a really easy take on how to disable the login sound.
Open a terminal windows and enter:
this opens a nautilus window with root privileges.
Now, head over to /usr/share/sounds/ubuntu/stereo
There are the sounds for the login, logout, error messages etc.
Search the “desktop-login.ogg”, make a backup (simply drag-and-drop the file to your desktop) and then delete it.
That’s all, the annoying sound is gone!
If you want to change the login sound, you have to convert the new login sound into the .ogg format and name it “desktop-login.ogg”. Drag-and-drop it into the stereo folder and you have a new sound.