My last practice test I had a similar problem. I didn't want to fart, but apprently the gas I had wasn't to be denied. I had eaten spaghetti for my last three meals with salad. I guess the lycopene/roughage combo was too much. Anyway, since my ass was clinched tighter than Fort Knox and the gas had to go somewhere, I couldn't help burping. They tasted like spaghetti, so I was afraid they might stink.
I have precedent for stinky burps. Off topic a bit, but at The Phantom of the Opera, I got a case of the stinky burps. During the intermission, my wife told me she kept smelling them. Strangely enough, the chic next to me at the show before the intermission had her husband sitting next to me after the intermission. I guess she needed a buffer zone.