I follow this guide to get my 5.1 audio working: https://help.ubuntu.com/community/DigitalAC-3Pulseaudio and it has been working for some time now in 18.04 (and before in 17.10)

Starting around Nov 13th? (could have been a bit earlier since I didn't reboot in a while) I noticed my audio stopped working. I noticed the profile for the card was no longer set correctly and I fixed it with pavucontrol.

I then noticed though the return of a very loud jarring glitchy sound that is emitted anytime a new audio stream is started (and when opening pavucontrol), but otherwise seems to be working. I can do the speaker test in the sound settings and hear all 6 speakers. Also I noticed sometimes when no audio is playing for a while, I start to hear a buzz, which goes away when a new audio stream is played (after the loud screech subsides).

I actually had the loud noise before and solved it by adding tsched=0 to my /etc/pulse/default.pa and /etc/pulse/system.pa file on this line: load-module module-udev-detect tsched=0 however this does not seem to be working anymore. I tried setting it to 1, or removing tsched with no effect.

I suspect some update caused this, but can't figure out which one. I tired reverting to 4.0.15-34 since it changed around that time, but for some reason, no audio devices show up with that kernel except "dummy", also networking does not work, even though I installed the -modules package as well.

Any tips on debugging this?