A noisy stomach by itself is a good thing, at least for my wife. As we were told, that means it is working.
A noisy stomach that causes pain is a bad thing, always get it checked because it will become a constant pain if ignored. It's the beginning of a flare up.
Through our experience, if my wife feels any discomfort for longer than day, she calls the doctor. Like anything else, catching it early is easier to settle down than if you were to wait.
Sometimes she has discomfort, but if it is gone the next day, we assumed it was something she ate.
Listen to your body and learn it's language. That's the best thing anyone with crohn's can do.