Linux Mint moved to a new sound server called Pipewire.

To check which sound server is running, use the following command:

inxi -A

If you're unable to get the sound working, you can try to go back to the older sound server called PulseAudio.

apt purge pipewire pipewire-bin
systemctl enable --user pulseaudio
sudo reboot

Upstream bug report for choppy sound over HDMI: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1025453

How To Fix Buzzing Speakers On Linux
https://inv.nadeko.net/watch?v=Kt0dkXWnaC4