How should I deal with a noisy eater?

For years now, I've had to deal with my mother and father eating very noisily with their mouths open. I guess as a child, I didn't mind, but now it irks me to no end - to the point that I eat my meals in a different room. Eventually, my dad asked why I kept avoiding the two at mealtimes, and I tried to explain, but he called me rude... And forgot a few days later, so I know that approach won't work. I really need some help with this, because they are my parents, after all. Does anybody have any ideas?