Just as a test I built the Castle Defender tutorial as an HTML5 project. In Chrome it works perfectly. In IE 10 no sound.
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I am running windows 8.
There are ogg and m4a files in the resource folder.
I also have the Flash Exporter installed.
I decided to convert the oggs to mp3s using Nero, so the resource folder now contained m4a, ogg, and mp3 files. This made no difference in IE.
I then decided to rebuild the HTML 5 Project so I ran build all, and it deleted the MP3s. It didn't touch the other files, just the MP3s.
That seemed peculiar to me. It still made no difference in IE. No sound. In Chrome - perfect sound.