If it is a must for you to embed audio files, then we suggest that you host the file elsewhere online. You can then use the following code to make this file load when the email is opened. You will need to replace the URL with the actual URL of the hosted audio file.
Explanation of Code Attributes:
AUTOSTART – When this is set to TRUE, the audio file will automatically play.
LOOP – If you want the audio file to play over and over again, set this to TRUE. If you want the audio file to only play once and then stop, you can remove this attribute completely.
WIDTH and HEIGHT – Setting this to "0" will ensure that your email shows no sign of the audio file.