Had the same thing happen with my 2008 3400RL. Turning the bathroom sink on then the kitchen would solve the problem. It only happened twice, and never again. Also, I don't remember if I turned the pump on, or just was using city water. I have since bought a water pressure regulator with a gauge on it to measure pressure. If it is below 40 I figure I might have a problem.
There is nothing I did to alleviate it except to do as you did and the problem went away.
Edited: You didn't buy my old 3400RL did you?