While waiting in line for lunch (sesame chicken and fried rice), I considered the music playing in my head and decided to listen to the world- something, I realized with some surprise, I rarely do.
I stopped playback and I started overloading immediately.
I don't think it was even a full minute before I turned my head-music back on. I repeated the experiment, this time in the quiet Gargoyle area, used as a much quieter eating area than the rest of the Food Court; I didn't hit immediate uncomfortable sensory overload as from in line, but I was immediately aware of the 60-cycle hum of the flourescent lights in a bad (read as: remarkably annoying) way.
So I learned something. My mind constantly loops music to mute the overload I otherwise get from trying to process all the sounds around me. I guess it's one of those semi-autistic things again, but I find the resistance I built against it interesting: give myself something easy to process auditorially so I don't get uncomfortable processing everything.