I converted a mono soundtrack on a video to stereo by unlinking the video and audio, exporting the audio and converting it to stereo using Audacity. I imported the stereo version of the sound track (in AIFF format) and used the Replace Clip From menu option to replace the existing mono audio with the imported stereo version. I then clicked and dragged around the video and audio tracks and relinked them.
The problem is that the audio does not track to the playhead when I move it. The video does but the audio continues to play from where I last left off. The only time when the audio and video are in sync is when the playhead is as the start of the video. When I then export the finished movie the audio quickly moves out of sync with the video - you can hear some sort of audio artefact at the time the two go out of sync.
What can I do to keep the audio and video in sync?
Try converting the audio to a WAV file rather than an AIFF before you import it into your project. (Premiere Elements doesn't do MP3s and AIFFs well.)