The Push IO Manager handles sound requests for you. No extra work is needed to play a sound from a push notification.
To facilitate playing a custom sound for your push notifications the following much be done:
Step 1: Include the sound file in your project.
Step 2: Add the sound file under the Copy Bundle resources section of the build phases tab for app target.
NOTE: The sound file must be included in your project and Responsys users who create push notifications must include the filetype (.wav, .caf, etc.) when entering the sound file name. Work with your marketing team to define the sounds they can use when they create their push notifications in Responsys.