I'm on 14.04 and I get volume spikes randomly. I first noticed it only when using Spotify so I thought it was a software issue with Spotify, now I've started it noticing sometimes when playing through flash as well so I'm thinking it has more likely to do with pulseaudio. Please help me troubleshoot this. What commands can I run to get you the information you need?
Update: I've now started getting the audio muted randomly and I haven't noticed the spikes in a while. There's nothing that I've done, no settings I've changed. But this is even more annoying since I used to be able to max out the volume in Ubuntu and control it with my external speakers instead, but when it get's muted there's nothing I can do to workaround it. Thoughts?
I had experienced exactly the same issue on my Debian Stretch some hours ago. If I read this report correctly then it seem that there are bugs with some motherboards and pulseaudio.
Follow this comment to verify in pulseaudio log that your problem is related with flaky jack sensing. If so then you may find other comments on that bug report helpful:
and:
This bug was reported in 2011 but comments from 2015-12 as well as my own issue confirm that it's still present.