As noted, some browsers restrict autoplay without some sort of interaction. The solution is to either add a button or start the sound after the first page (navigating to the next page is the interaction in this case). If selecting "Play in Background" doesn't work to play across pages, try this .js which you'll attach as a resource:
stopAllMedia = function (targ) {
if(!targ) targ = document;
$(targ).find('audio,video').each(function() {
var media = $(this)[0], player = media.player || media;
if($(this).parents('.page').index() == 0) return false;
try{player.pause(); media.currentTime = 0;}catch(e){}
});
}