I just did:
$ systemctl enable rpcbind
And this caused the volume on my headphones to increase severly.
First off, I don't understand why this happens, as rpcbind seems completely unrelated to my sound? Issuing the command a second time doesn't change the sound, and neither does
Secondly, I would like to prevent this from happening again; the volume jumped more than a little bit (some panicky actions to remove my headphones accompanied by a loud expletive followed).
This is not the first time I've noticed that systemd commands change my volume by the way... I was playing a HTML5
<audio> tag in Firefox through pulseaudio. I'm running Arch Linux (updated).