Rhythmbox is silent?
After playing around with different Linux Shells/UIs/window managers (including i3, Gnome Shell, etc) and some frequent restarts, I noticed that for some reason my music player Rhythmbox had stopped playing any sounds. Though it was still “playing” songs, no sounds were actually made by speakers, headphones, etc. In contrast, all other sounds were OK, including OS sounds like info/error messages, or other players like VLC. Changing sound setting, volumes, as well as changing audio devices did not have any effect on this.
Resetting pulseaudio configuration
Turns out that the pulseaudio configuration was messed up. The solution to this problem is to move/delete the old configuration, then let it be recreated (the original problem description and solution to this is here):
mv ~/.config/pulse/ ~/.config/pulse_old/ # move/delete the old config pulseaudio -k # restart pulseaudio
After doing this and restarting Rhythmbox its sound should be back to normal, – though you might need to restart the OS if you run into problems with external speakers/headphones.