I don't know about the cheering, but they mute the sound during the music because of broadcast rights. The candidate may have rights to use the songs for rallies, but broadcast rights would be a different contract and fee schedule and would probably be the responsibility of the broadcaster to obtain rather than the campaign.
If someone plays a song during an event that you are covering as a news you would think it would be fair use, but maybe it has never been court tested and they are playing it safe.
Thanks I hadn’t thought of that angle, and you’re almost certainly correct.
Dang, I really like that rousing music at the end of the speech. And the crowds, my God, the crowds.