I have a question concerning the snake on my Met Pro. Sometimes when the ball goes in the mouth (and settles in) I get a SNAKE letter credit (that shows on the screen) toward multiball. Many times, however, it just makes a hissing sound and I no letter credit. This is not normal is it? The switch seems to be in good shape. This may or may not have started with the last code up date. Any information will be greatly appreciated.