I'm running Rhythmbox 3.4.2 (the latest version in Synaptic) on 18.04.6 LTS 32-bit.
The application opens without any apparent issues, my Music Library loads fine, and I can select and 'play' any of the tracks (both MP3 and WMA). However, there is no sound. This is a recent problem which now happens most of the time, although sound will randomly return without me doing anything.
I've tried uninstalling and reinstalling Rhythmbox, and I've made sure that the application isn't muted in the sound settings.
Related packages that are installed and up to date are:
The same issue also affects Clementine. By contrast, there's always sound when using VLC or Audacious to play music files.
If anybody has any suggestions for a fix, I'd be very grateful.