Sounds like a dirty or misgapped switch in the score motor or relay. I dont know the schematics of that game but that's where I would start. Make sure the switches are gapped properly and when the close they make a good connection.

So it doesn't move at start but works fine during the game? Does sound like the motor in the bottom of the cab. Dont know what it's called. My mars trek did that when I got it. Guess I was lucky, I just had to clean the stacks and regap them. Been working since.