There is a specialised forum for FM Go (see the Forum buttons at the top). You might find someone with an answer quicker there (you seem to have done everything correctly in FM11)
Can you enter the sound on the iPad, as opposed to the Mac?
Thank you for your post. I answered your identical post on the FileMaker Go forum at:
In essence, FileMaker Go will not play Sound files in a Container field, nor are you able to record sound files. Our Development and Software Quality Assurance (Testing) departments are aware of this limitation. No other information is available at this time.