http://www.androidpolice.com/2013/08/14/bug-watch-android-4-3-automatic-looping-of-sounds-with-soundpool-is-broken-may-cause-some-games-and-apps-to-be-eerily-quiet/
It will be fixed in next system update. I'm trying to find a workaround to make it work before that.
For now, here are things you can do if you are affected:
- Use Android version 4.2.2 for now.
- Upgrade to latest custom 4.3 (quite complicated).
- Wait for us to find a workaround.
- Wait for google to release official update (should be soon, you can check for it in Settings->About device->System update menu)