I had Realtrax switches at one time, and when you said the motor chatters when the train passes through the switch, I remember that I had to check the gap of the isolated rails. Even though they're isolated, they are close to each other and any little fragment of conductive material falling into the gap will make connection and it's not isolated any more. I took a small screwdriver and gently pushed one of the rails slightly to enlarge the gap. Then I cleaned the gap thoroughly, and the problem would go away.
It's worth a try.
Mike
