The problem is to do with mobiles' policy of only allowing sound to play in response to a user input.
eg: Autoplay audio on mobile safari
This is a limitation in mobile browsers.
Sound must be played in response to user interaction, hence why it automatically does not play, but does upon touching pause then play.
A solution would be to implement a welcome screen that loads the sound upon hitting an 'enter' button, as the top comment of the above link describes.