Sound Track Pro, Audio not Sinked with Visual file

Hi all.
I am doing a project in Sound Track Pro. I am editing a lecture, and I have edited to about the 15 minuet mark. Yesterday I got done and quick STP. I come back today and where I left off, the audio does not match up with the visual sound file in my timeline. Its off a bit. Where I can see silence in the audio file, the voice is still talking etc. Does anyone know what happened? Or how to sink it back up with the visual audio file?

Caleb