From what I've seen, if it loads ok, but you are getting random freezing like that throughout the game, its usually a problem with the media (or the drive). Is it freezing and locking up requiring a reset, or just doing the pixelating type freeze?
For some reason with Super Mario Galaxy and a few high graphics games, I've seen pixelating at certain points in the game when theres alot of graphics involved. It was explained to me that this was due to the fact that the original game was a double layer 8+ gb DVD, compressed to fit on a single layer 4.5gb disc.
But I have not seen that with MadWorld. Try a different manufacturer of DVDs. Which writer software are you using?