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On my laptop I have seen once a week or so an issue whereby the system tray and GUI elements of KDE will show that the system is unmuted yet no audio plays.
If I right click on the mixer system tray icon (officially this is called "volumeicon") and open alsamixer, I can see "MM" so it really is muted.
Ultimately the problem is caused by our good old friend, a race condition, between PulseAudio and volumeicon upon logging in.
The fix is to run the commands below:
pkill volumeicon
sed -i 's/^card=default$/card=pulse/' ~/.config/volumeicon/volumeicon
setsid -f volumeicon
Basically ensures volumeicon always connects to the correct audio card no matter if it started before or after pulseaudio. Yay!
Disclaimer: I have only done basic testing on this but it seems to have fixed the problem for me.
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