What are you editing, and is your source video/audio in sync?
Exactly what is INSIDE the video you are editing?
Codec & Format information, with 2 links inside for you to read http://forums.adobe.com/thread/1270588
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
https://forums.adobe.com/thread/1070933 for screen shot instructions
Free programs to get file information for PC/Mac http://mediaarea.net/en/MediaInfo/Download
Does your video use a VARIABLE Frame Rate or a Constant Frame Rate?
What version of Premiere Elements and on what computer operating system is it running?
Properties of your source on the Timeline is important. For a quick look at the video audio properties, please tell us the brand/model/settings for the camera that recorded that video.
1. Export settings
2. Import settings