As I understand it, the audio capabilities in Motion are rather limited as it is pretty much a separate app that is included so you can hear audio while animating. To see how it is separate, put an audio clip in your project and start playing it. Next bring up the audio editor in the timing pane. There is a separate playhead and play button. When the playhead is halfway through the minitimeline click on the play button in the audio editor. 2 copies should now be playing out of sync.