What model of camcorder is this video coming from and what format and resolution is it?
When you add your video to your project, are you waiting for them to fully conform (as indicated at the bottom of the program's interface) before you begin editing?
Try clearing the video from your project and reimporting it into your project -- and then wait for it to fully conform before you play or edit it.
Welcome to the forum.
Along with the answers to Steve's questions, as he points out, Conforming of the Audio is very important, and failure to let that complete is one of the main causes for truncated Audio. For more info, see this Tips & Tricks article: http://forums.adobe.com/message/4330843#4330843
Good luck, and please let us all know a bit more.