You are describing the typical behavior when the create frame table routine hasn't been done.
* Open the movie file in the Timeline mode
* Right-click the movie track (track 1)
* The top option will be Recreate frame table (I don't remember the exact words)
This will do some mysterious function that syncs up the audio and video. Fortunately, you only have to do this once.
Sorry to hear Scotamberg wasn't helped by siglermalzes answer, but I sure was! I had the same sync problem, getting worse by the second.. Performing the "create frame table" function completely solved my problem. Thanks!