The background music plays even when I am not playing in a world.
That is, when I am at the screen that has the buttons:
Single Player, Multiplayer, Options, Quit game.

I find this to be extremely annoying when I wish to handle some other task such as answering the telephone or talk to someone or work on some other program running on my computer.

As far as I'm concerned the sound effects shouldn't play if Minecraft doesn't have Windows focus.
That is, I'd like to see sound effects (especially music) muted when I hit Escape to pause the game, when I save and exit a world, and when the Minecraft window in minimized.

I like the background music while playing the game but right now I have to leave it turned off because of this behavior.