I used to work for Toys R Us, so here's a random anecdote no one asked for. When you called the store and were put on hold there would obviously be hold music. The music that played? It was the same music that was playing in the store. I remember calling in one day to get my shift assignment and the music was super weird, I told me coworker and he was like "yeah that's the music they are blasting in here, it's awful."

That's pretty common, a lot of older phone systems will literally have a line input where you can hook up a looping music player, Muzak receiver, a radio (illegal but common anyways), or whatever else to provide the hold music feed and for the most part if the business has overhead audio they'll want to use that as their hold music as well.