I recently added a couple of ringtones and notification sounds to my phone by placing them into my storage's Ringtone and Notification directories respectively, and I can select them from the sound settings dialogs without any problem.
The thing is that they also appear as songs on my Google Play Music's playlists, and of course I don't want to hear a 1 second long "jigglypuff!" notification sound every now and then when I'm listening to my music on shuffle.
I did search using Google for a while but it seems that there's no way of either removing the file from just the music database or from excluding those directories from the media search. I recall this didn't happen on an old 4.0 Sony Xperia phone I had with it's music player.