Erratic Vaccum Reading

Interesting. I notice when I adjust my 4 corner idle with gauge, and the vacuum goes up, it will get to a point where it "whistles" through the carb, like it is sucking a lot of air. Then, if I idle it down with the idle adjustment screw, it will stop. Is this strange, or am I missing something here. I appreciate all of this valuable feedback, as you guys are always on the money!