Whistling holley 1920

So I have a new(to me) 68 dart with a 225 and the carb whistles. It's annoying!:D. I have replaced the base gasket, sprayed carb cleaner all over it to see if the idle changes etc. The whistle is definitely coming from inside the carb. So today I took the carb off and turned it upside down and I noticed there is a hole drilled in the throttle plate. In all the pictures of holley 1920's I can find there is no extra hole. Is the hole supposed to be there? Do you guys think that's where my whistle is coming from? Do any of you guys have any insight into my situation before it slowly drives me insane?? Seriously, any help is greatly appreciated. It really is annoying. Thanks all.:prayer: