The notification sound at no connection is unfortunately not changeable via the settings.
It is possible that this tone is heard after a reset or update of a modem.
Often modem updates are done at night and the no connection tone can be irritating and cause people to wake up.
This can be solved by simply plugging in a headset, this way the sound goes through the headset and no longer comes out of the speaker.
Should you have any further questions, you can always contact us via this website.
Please mention the complaint clearly so we can serve you well.