Cannot mark my video with CC SA licence because Youtube Content ID found 3rd party soundtrack which itself is CC SA licensed It seems, I'm in a catch-22 situation. I took a song from Free Music Archive website. I was careful to find a song which does not contain No-Derivatives rule. The licence of the song says:
Attribution-NonCommercial-ShareAlike 3.0 International License.

My video is not being used for commercial purposes, so as far as I understand, I'm good to go as long as I add the same licence to my video, right?

And here is the problem. When I uploaded my video, Youtube immediately recognized the correct author and title of the song and said that my video contains a song from a 3rd party, thus I might have trouble:


  Your video has copyrighted audio that may affect its availability. You may be able to fix this by removing a copyright-claimed song below. 


I decided to ignore it and just change the licence setting for my video from Standard Youtube Licence to Creative Common licence to comply with the Share-Alike rule of the soundtrack. Surprise! Youtube seemed to ignore the licence setting. When I looked for more info I found that I cannot change licence for videos which have been marked suspicious by Content ID:


  You cannot mark your video with the Creative Commons license if there
  is a Content ID claim on it.


This means, that I cannot mark my video with proper licence to comply with the song author's licence, thus I'm violating the licence because Content ID doesn't let me change it.

What should I do? Is it enough to just add a note in the description: "Please ignore the licence setting - this video is actually licensed under CC SA NC licence"?

Of course, I could find another song, but what if Youtube Content ID will recognize every song from Free Music Archive and again mark my video as suspicious and prevent me from setting the correct licence for it?

What's even more strange is that Youtube says:


  Ads may appear on your video due to the presence of this song.


Hm, isn't Youtube itself then violating the NonCommercial rule of the song author's licence by adding ads to it?
I am not a laywer, but my limited understanding of the situation is this.

I see two issues here:


When you upload a video to youtube you need to grant them certain rights. As Youtube is without any doubt a commercial plattform, beyond others you have to grant them the right to commercially use your video. 
Unfortunately, as your soundtrack is CC NC, you didn't have the right to do so yourself. That's why Youtube is correct in complaining about the song.
"SA" means you have to share your work also as CC SA NC. As Youtube doesn't allow you to select that exact license, it's technically impossible for you to comply with that condition. 
(When you select CC-BY in Youtube, an additional license claim anywhere else, e.g. in the video description, would probably not legally binding)


So after all - if you want to upload a video to Youtube, it must contain only material that


has been created or licensed by you
is under CC BY license
is public domain or CC-0