How to Stop Annoying Notification Sounds

[Cerberus Bindweed]

How the heck do you turn off the annoying notifcation sounds on Steam.
I have gone into Steam > Setting > Notifications.
# I have set Show Notification Toasts to - Never
# Play a sound when a notification toast is displayed - OFF
# Friend Notifications are ALL turned Off.
# Flash Window when I receive a chat message is set to NEVER.
# Steam Notifications are ALL off.
# Family Notifications is also Off.

Yet I am still getting this annoying as hell Steam notification sound.

[xBCxRangers]

Go to settings, and Audio, and Disable UI sounds.

[ReBoot]

On which occasion?