Since my last pacman -Syu the kde system notifications do not work.
I have done the
cp -s libFLAC.so.6.0.1 libFLAC.so.4
and my test sound button works ok so does my alsa setup etc.
I can even change to an external player for the notifications to use noatun and kaboodle but the default does not make a sound.
ln -s libFLAC.so.6.0.1 libFLAC.so.4
I am not sure about using cp (copy). "ln -s" creates a symbolic link. You might want to remove whatever the "cp -s" created in /usr/lib before you create the link.