Try the following code (sorry, I didn't test it):
$("#messageCenter area").on( "click", function() {
var audio = $('#audio');
var lastSound = audio.data('lastSound');
if (lastSound) lastSound.pause();
var source = "assets/audio/" + $(this).attr('id') + ".wav";
var sound = new Audio(source);
sound.play();
audio.data('lastSound', sound);
});