YouTube’s automated system scans for copyrighted music upon upload. If it finds any, a Content ID Claim is sent from YouTube on behalf of the person or organization that owns the copyright to the music you included in your video.
If you have a Track Club subscription and have cleared your channel, any claims will clear before they're sent to you, leaving you to monetize your video.
Having problems with a claim even though you've cleared your channel on Track Club? Reach out to us at hello@trackclub.com.