Background sound starts automatically when your page loads up.
To add the background sound to your web page:
Select View / Visual Web Designer from the menu, and
Select Format / Page Properties from the menu. The Page Properties dialog appears.
Click on the button located right of the Background sound field to select the sound file. Check the Loop option if you wish to play the file continuously, and
Select 
button located right of the Background sound field to select the sound file. Check the Loop option if you wish to play the file continuously, and