Comment 3 for bug 1728587

I just found a fix here:
https://bugs.launchpad.net/ubuntu/+source/pulseaudio/+bug/1720519

You have to remove and reinstall alsa-base and pulseaudio.

I figured it out when I tried to start pulseaudio directly, and got this error message:

W: [pulseaudio] module.c: module-combine is deprecated: Please use module-combine-sink instead of module-combine!
W: [pulseaudio] module-combine.c: We will now load module-combine-sink. Please make sure to remove module-combine from your configuration.
E: [pulseaudio] module.c: Module "module-switch-on-connect" should be loaded once at most. Refusing to load.
E: [pulseaudio] main.c: Module load failed.
E: [pulseaudio] main.c: Hintergrunddienst konnte nicht initialisiert werden.

After
sudo apt-get remove --purge alsa-base pulseaudio
sudo apt-get install alsa-base pulseaudio
sudo alsa force-reload

It works again.