Sounds like there is a vacuum leak somewhere.

The thermoquad on my old junker truck whistles at idle speed, I finally figured that it is the primary throttle bushing (if it has any) on the left (linkage) side, raising the idle just slightly quiets it, so for now that is what I have done.

It also seems to have an internal leak, but it runs and starts like it is fuel injected, even cold, so thus far I have left it alone, but my mileage sucks, due to what must be , duh, the internal leak!

How much use has your carb seen?

Just a thought ...