That's right - I don't feel anything when I am eating myself, or even when I am at a lunch table with others munching with me. It's only when I am not the one eating. I also get irritated when I am on the phone and the person at the other end is chewing or lapping.

Also, I don't think it's cultural and I suspect it might be hereditary.

I think I suffer from the same symptoms, but weirdly enough, if I'm at table and I got food, there is no problem.

Even if I finish first and the other are still eating, it's really only when I didn't eat / not eating that it infuriate me.

Interesting. What if you listen to a recording of yourself eating? While you're at if see how much you can distort it before it stops or starts to bother you. E.g. Played backwards, at double speed, half speed, etc.

Yeah, doesn't bother me. Never bothered by the sound of my own eating.