I have a 2000 426 that has a knock in it that I can't seem to find. When it is at idle or chugging it sounds a little like a small marble bouncing around in the lower front of the motor. I am thinking that it might have something to do with the balancer shaft or water pump but both appear to be fine. Is the water pump shaft supposed to have any play in the balancer shaft? I can wiggle the water pump a little back and forth. I've gone through the motor and everything else checks out to be in clearances. Any help or ideas would be greatly appreciated!