Whistling sound coming from the carb, right at tip-in ('71 318, Holley 2 Bbl).

Any chance it's the PCV valve? I've heard plenty of those whistling......Especially the aftermarket ones.

I can't remember a whistle, but sure believe it could, lotsa ones that rattled like crazy .
Pull it outta the cover, or disconnect and plug hose, and listen.
I'm pretty sure that's coming from carb .
Just push, lean your weight on the carb, it'll prob stop or change .
Good hunting, lol