Sorry, I'm not posting the maps, they're part of my mod. I've told you everything about the setup, and there's not much to it...trigger_cdaudio has only two properties. I've used one entity to turn on track 24, and the other is set to "stop".
Maybe I'll decompile a Half-Life map later and see if they did it differently.
Edit: Okay, I think I might know what it is. The player is teleported into a dark box before the level changes, and is standing inside the trigger_cdaudio (the one that's supposed to turn the song off) when the change occurs. Maybe that has something to do with it, I don't know. Also, when the map starts, the player is immediately spawned inside the trigger_cdaudio that makes the music start. That might cause the looping, so I'll try triggering it with a trigger_auto one second after the level starts.These are complete guesses, but who knows.
Edit 2: Well, my sound is still continuing into the following map after the level change, but that fixed the looping problem at least. :