Quoted from accidental:+1 on the Stern knocker chirp. Nothing short of embarrassing. It boggles my mind why the market hasn't demanded, and succeeded, in ensuring that Stern put a real knocker in every game. It is one of the non-negotiable heart and soul aspects of pinball history IMO.
At least for the price of the premium/ le , put it in them . I would consider it a plus when spending the extra cash over the pro.