Question: This is a bit mysterious problem.

I upgraded Ubuntu 14.04 to 16.04. Now after each reboot the sound volume resets to 100%.

It is mysterious because it happens only on one computer, on another the sound volume is saved OK.

The other mystery is that I have Ubuntu 14.04 and 16.04 on the same computer with the common `/home`. On Ubuntu 14.04 the sound is aved OK, but on 16.04 it does not.

What can I do to troubleshoot this issue?

Answer: 
I created a new user and found that sound works correctly with the new user. That means that something was wrong in user configs. I found some configs and it looks like the problem is solved. The files were not in text format and I have no idea what that format is.

I removed all files from `~/.config/pulse/` and rebooted. Now it works OK.

I also removed all files from `/root/.config/pulse/` to fix 100% volume on login screen.

I think they've changed format of some config files in the new version of `pulseaudio`. The config from 14.04 confused `pulseaudio` in some way.

I saw some bug reports about this issue. It may happen when you replace Ubuntu versions with the same `/home`. 

**Update:** This looks like a distro upgrading bug. I upgraded 14.04 to 16.04 on another computer, and there was the same issue.

`cookie` file needs to be removed in `~/.config/pulse/` after an upgrade.
Disable the "Keep Settings" in the PulseAudio Equalizer.