1st, need hardware and device driver details... and lots of other questions
2nd, CS6 Bug AVCHD http://forums.adobe.com/thread/1004369?tstart=0
-and LOCK the media http://forums.adobe.com/thread/1077245
Let's start with a simple question. What media player are you using to play back the file?
windows media player
Try downloading VLC and see if it will play the file correctly, in my personal experince WMP doesn't play the audio from my AVCHD cameras. Below is the download link.