CARL LANGE also showed how to get hidden, autoplaying audio in html5 on a iOS device. Works for me.
In HTML,
<div id="hideme">
<audio id="audioTag" controls>
<source src="/path/to/audio.mp3">
</audio>
</div>
with JS
<script type="text/javascript">
window.onload = function() {
var audioEl = document.getElementById("audioTag");
audioEl.load();
audioEl.play();
};
</script>
In CSS,
#hideme {display: none;}