We really need more information e.g. what files are you burning and how they were created e.g. are they recorded from a TV card, is it a copy of another DVD etc.
Often self-made recordings suffer audio sync issues depending on how the codecs used (if you use a codec which creates a good quality hi-res picture, this takes a lot of CPU processing time, and sometimes video frames are dropped, causing the audio to go out of sync. Using a codec which gives a lesser quality picture may not drop frames etc.)