Funny, we usually enjoy bodily functions to thier fullest extent.
If it bugs you that much, though, be rude. The guy is, after all, an intern. After each belch, a loud "excuse you!" might be in order. Maybe a nasty "do you mind, I'm working?" We don't have interns, but we do have trainees. When necessary (not just because I'm an ahole), I am not afraid to belittle, embarass, or verbally rough them up. Being in a high-pressure environment, though, that's typically to be expected.