So no luck with traps I guess. Sorry for bumping this, but have you tried any repellents? I mean not only substances, both chemical and natural ones, but also ultrasonic devices. I heard a lot about it and even tried one to repel squirrels from my backyard. As far as I know, the devices like this should work with rats and chipmunks as well. Here's I guess you should try it too, here's guide on wikihow.