Comment 39 for bug 1799007

Yes, I suspected as much. System76 wouldn't ship a laptop without working audio on Ubuntu.

It sounds like that machine has gone through a couple of upgrades:

  DistroRelease: Pop!_OS 18.10
  InstallationDate: Installed on 2018-03-05 (230 days ago)
  InstallationMedia: Ubuntu 17.10 "Artful Aardvark" - Release amd64 (20180105.1)

I can't tell what has been broken in the process, but it does look like pulseaudio since 'pacmd' isn't working for you.

I suggest:

 (a) Try to reinstall pulseaudio packages, like:
     sudo apt install --reinstall pulseaudio

or

 (b) Back up your data and then reinstall fresh from http://releases.ubuntu.com/18.10/

We may never know what went wrong on the machine before 18.10 reaches end of life in July 2019.