Maybe your PC is missing an AC3 audio codec and your DVD has an AC3 audio stream. Or it could be DTS surround sound audio.
Try encoding the audio as mpg1-level 2. Or if you can afford the extra file size, LPCM.
Fav quote - "Experience is whatcha don't get 'till ya don't need it no more."
System - Athlon 1.4GHz, Win98, Hauppauge PVR250 receiver and compressor.
Software -Magix Movie Edit Pro 10, Nero 6 + NeroVision Express, Moho 4.61, PSP 8.1, Bryce, Quicktime 6.52 pro, Goldwave 5, DVD-Lab.
Cameras - Panasonic GS9, Canon ES8400V, Canon EOS D20 and Canon A70