Movement Noise Question

[chris_nor_cal]

I've got a question. Why does my Z Series Sub-Date's movement make different noises while I have it pressed up against my ear--it's not a constant sound, every once in a while it changes its tune. I don't know much of anything about the technical inner workings of a watch, but is this normal? Why does it do this? I would think it would only sound different when the hands move/ or date skips