What is the source of this Video?
Cable
Sat
DVD
VHS
DVR
PC hooked to TV playing video's?
If it's a PC what program are you using to play the file? What is the file type? Download GSpot to get info about the video clip. What Codec Pack are you using (DefilerPak is the best)?

I have many clips and only a few are out of sync. Good programs will let you change the audio offset + or -