I'm not sure how your card works, but when converting video into a DVD compliant format, it splits the video and audio streams.
So for instace you save footage under the name of snelly, it will save 2 files.
snelly.m2v ( Video )
snelly.mpg ( audio )
so if you try & play these back it will only play either the video orthe audio.
I think this could be your problem
Or if it is capturing it as an AVI file, then it could well be the codec being used or how the audio is being sampled. If it being converted into a PCM stream this could also be causing issues. I capture all my audio in stereo.