Unfortunately, the music around property fluctuates all of the time (check out Spaceship Earth next time). In fact, sometimes even the music fluctuates. As an example, every so often, the music normally played around the fast-pass area to Big Thunder Mountain will change to the normal Frontierland loop. I've heard this at least 10 times over the past two years. I've also noticed this happening in other places as well.
Disney is supposed to check the audio levels (each piece has a documented level that it's supposed to play at) on a regular basis. However, as with most things, this may not be happening as frequently as it should be.