Comment 1 for bug 1636905

Seems like the problem has been partially resolved:

I did not mention that I had a dual boot machine with Windows 10, since I did not think
it was relevant. Now, here is what I did:

I first reinstalled Ubuntu 16.04 (erased the Ubuntu 16.10 partition).
When I logged into Ubuntu 16.04 the sound problem was still there.
I then logged into Windows 10 an suddenly realized that the sound problem was also present in
Windows 10. So I now suspected it might be a hardware issue and not related to Ubuntu at all.
But before ordering service on the machine I decided to try to reinstall Windows 10 also.
From Windows, I selected "Reset Windows" (option "Remove everything").
After logging back into Windows 10 after the reset, the sound problem was still there, but
the same day I was about to ship the laptop for service, I logged back into Windows a last time,
and, voila, the sound problem was suddenly gone.

I then logged back into Ubuntu 16.04, and to my great relief the sound was now working from Ubuntu also!

So then it was not a hardware issue, but what was it then? If I should guess now, the problem could maybe be related to the external interface connector on the Dell laptop. Since it is a multipurpose microphone in/stereo headphones/external speakers/headset connector it might have confused Ubuntu?

The reason is: Each time I try to connect the headphones in Ubuntu I get a popup dialog asking what audio device I am trying to connect. If I choose headphones it works fine until the next reboot. After that I need to unplug them and replug them for sound to start working again.

The problem could also be related to Ubuntu 16.10 vs. Ubuntu 16.04. To check this I would have to reinstall Ubuntu 16.10, but I do not have the courage to do that currently..