On listening to music

Why do we listen to music?
Is it because of the emotions it inspires us?  Sometimes I listen to music because it matches the mood I am in, and therefore seems to sympathize with me in that moment.
Other times I listen to music to inspire a new mood.  "Pump-up music" for example.
Most of the time though, I listen to music because there is something pleasurable, that I myself cannot explain, that comes from certain tones and beats in succession entering our ear.  I can't tell you why this happens, it just does. At least for me.  I know of a few people who generally are disinterested in listening to music.

If you have any ideas what happens to be so pleasurable about listening to music, comment it.  I'll let you know if I ever figure it out.