For quite a while now, I’ve been annoyed by the system notification volume going to 100% on my Debian systems, regardless of my attempts to set it to a lower level. For example, when I open the KDE System Settings app, change something, then try to close the window, the sound that accompanies the save/discard/cancel alert is always startlingly loud. I think I have finally found a fix: in your /etc/pulse/daemon.conf, put in a line saying flat-volumes = no (You should find an existing comment “; flat-volumes = yes” that indicates the default.) You can make this new setting take effect in the current session immediately without having to logout or reboot, by executing the following as the currently-logged-in user: pulseaudio -k (This kills and restarts the PulseAudio daemon for your user session.) There are several discussions of the pros and cons of this issue online, going back some years. For example, here <https://bugzilla.redhat.com/show_bug.cgi?id=1265267>. Also a mention about the “flat-volumes” setting in the ever-reliable Arch Linux Wiki here <https://wiki.archlinux.org/index.php/PulseAudio>.