I actually have the same issue. The reason why it is being flagged is not the music in my case. It's the fact that I cannot provide a link or written statement that Musegames is ok with me monetizing their content (for all the 3 cents that'd probably give me in a year...
I actually keep most of my vids ad-free, the GOIO one just took another vids default for reasons only YT knows.).
Still: It would be nice if such a statment could be posted somewhere on the forum - or if you are NOT ok with it, to let us know.
It is as easy as copying the statement Notch made for Minecraft, I guess.
If such an official statement exists and I missed it, please point me into the right direction.