If all your sound devices disappear on Ubuntu (especially after upgrading the kernel), then run this:
sudo apt-get install linux-modules-extra-`uname -r`
https://askubuntu.com/questions/1230363/internal-speaker-audio-is-not-working-in-ubuntu-20-04-lts-after-upgrading-from/1323133#1323133
On Linux at random times I get static from any audio playback. It's exactly the symptoms here: https://askubuntu.com/questions/1066565/static-noise-when-playing-sound (staticy, random, lingers). The fix is pulseaudio -k.
Sometimes in a movie via parole the dialog disappears or is very quiet, even though the music is normal. Or with mpv it happens right from the start. This (https://github.com/mpv-player/mpv/issues/6563) gets it back:
mpv --af=lavfi="loudnorm=I=-16" the-movie-file