I don’t want my login screen to beep. So I looked for a way to mute it. I couldn’t find a way to do this over a menu or another configuration. After looking a while I decided to move the soundfile away by the following command
sudo mv /usr/share/sounds/ubuntu/stereo/system-ready.ogg /usr/share/sounds/ubuntu/stereo/system-ready.ogg.old
Now my login screen is silent =)