What kind of output? PDF? Flash? EPUB Reflowable? EPUB Fixed Layout? Publish Online?
What computer platform?
Place an MP3 file on your starting page. Put in the most inconspicuous spot you can (but Publish Online will display a small "player" icon that allows you to turn the soud off; you can't change that).
(1) Open the Media panel (Window > Interactive > Media). Give it no preview image and check Play on Page Load.
(2) Preview in the EPUB Interactivity Preview panel (Window > Interactivity > EPUB Interactivity Preview).
(3) Upload to Publish Online and open the file. The "player" will look like this: