Congratulations! Since you finished the zone, you have seen it all - each zone must be explored entirely to be completed.
No, the music cannot be disabled (sorry).
:D
That happens to me when I'm overly tired, and it can happen with any music heard any time during the past day(s) (e.g. the jingle of a commercial). When it comes to games, I can't remember if it ever happened, even when playing demanding games for hours (for example, Last Ninja 2) - but it's ages since I actually did that, so I might be misremembering.