I usually turn the alert sound (by default a water drop sound) off by going to control-center→Sound→Sound Effects and muting the Alert volume. This is in Gnome.
I wanted to turn it off in a custom live build of Debian by default, but I can't figure where this setting is stored. I tried dconf and looked around config directories extensively without success. I tried
find ~ -mmin -1 also
gio monitor and
inotifywatch without success. The only output by
find ~ -mmin -1 was
.config/dconf/user which get edited all the time the control center is opened anyway. I replaced this user file in a vm to test and all dconf settings were updated except the one I need (the alert sound). I also tried
dconf watch / which gave no output when I tried editing the alert sound setting
I'd like someone to tell me how to mute this setting from command line and possibly tell me where it is stored.