I just called the contractor who installed it. He said it's just that it's an older house and the wiring can't be split. I've got four rooms on one circuit - kitchen, living room, bathroom, and my son's room. He said now they put in 4 circuits for the kitchen alone. He said if it pops when nothing with a big power draw is turned on, then it's something to worry about, but when it pops when I've got something running, it's actually doing it's job and preventing a safety hazard. Damn nuisance, that's what it is.

I realized that it started popping around the same time I bought a slightly more powerful microwave and plugged it in to a different outlet than the old one. If I plug it into the outlet with the fridge, which is on a different circuit, it doesn't pop.