Homebrew Some DVDs don't play sound in WiiMC

[Derpstick]

The TV that I have my Wii hooked up to doesn't have a DVD player, but I found out about WiiMC, which you can use to play DVDs. I put in a DVD, the menu showed up and the audio played. After mashing all the Wiimote buttons trying to see which one would play it, the film started playing, but there was no sound. I did the same with a different DVD, and this time the film's audio did work. The disc I used the first time was a bit smudged, but I'm not sure whether there was enough to stop the audio, since that same disc was working fine in a real DVD player just yesterday. What is causing this? (and how do I navigate the menus?)