I just purchased a Stern Mustang LE. I thought something was wrong when I pressed "end" after entering my initials for high score, there was this terrible screech. I thought it was going to blow the speakers. It wasn't until we had a match for free game that I realized this is what Stern came up with to replace the knocker. I read some threads that indicated I could turn this off in settings, but the only setting I can find is to activate the knocker. How do I de-activate the knocker?