I am assuming that you are working with Photoshop Elements 12 and Premiere Elements 12. On what computer operating system are they running?
Can you open your .avi file in the Elements Organizer 12 and playback the file there and hear audio in the playback?
We have just helped a Premiere Elements user resolve a no sound with .avi file in another thread. Her answer was to update Premiere Elements 12 to 12.1 (See opened project Help Menu/Update.) Why is there no sound on avi files?
The details are in the link cited in my conversions with the user Vickie.
The full video and audio properties of the problem files are needed to evaluate situation such as you describe. In the case of the other user, she was not able to give us anything beyond .avi file. But, fortuately that 12.0 to 12.1 suggestion came to the rescue nonetheless. Bottom line is that, if the 12.0 to 12.1 Update does not resolve your issue, then we will need to go "by the book" and gather file properties, project settings, and the like to try to target the cause of your audio issue. Have you added to this project any narration clips from the program's Narration Tool?
If you create a new project, can you hear the audio from this .avi file in it? Is the problem confined to one .avi file or to any of these .avi files that you import into new or pre-existing projects. Can you hear the audio from non .avi files?
Looking forward to your follow up.