Welcome to the forum.
When you look at the Waveform Display of that Clip's Audio, does it show "flat-line" at that point?
The most common cause for truncated Audio is that the Conforming process was interrupted, and did not complete. See this ARTICLE for more info on the Conforming process.
Also, if not conforming, much more information is needed
Read Bill Hunt on a file type as WRAPPER http://forums.adobe.com/thread/440037
What is a CODEC... a Primer http://forums.adobe.com/thread/546811
What CODEC is INSIDE that file? http://forums.adobe.com/thread/440037
Report back with the codec details of your file, use the programs below... a screen
shot works well to SHOW people what you are doing
For PC http://www.headbands.com/gspot/ or http://mediainfo.sourceforge.net/en
For Mac http://mediainspector.massanti.com/
If you have a red line over the timeline after importing a video and before adding any
effects... your project is wrong for your video... read above about codecs
Once you know exactly what it is you are editing, report back with that information...
and your project setting, and if there is a red line above the video in the timeline,
which indicates a mismatch between video and project
More information needed for someone to help... click these links and provided the
For CS5 and later, the easy way to insure that your video and your project match
See 2nd post for picture of NEW ITEM process http://forums.adobe.com/thread/872666