It seems reasonable to me to say that soundwaves exist in the world, but music only exists in our brains. There is something added in our perception of the soundwaves that turns them into music.
Something exits in the world, it seems. Sound waves and music are merely our interpretation of it. Maybe what actually exists in the world is music, and sound waves are what our brain invents when the music is too complex for it to grasp?
I guess my point is that sound waves are not terribly controversial. A simple device can measure sound waves present in the air. It would be much more difficult to build a device that told you whether music was playing. Reasonable people could disagree about whether certain sound waves constitute music or noise.