Edelbrock 1406 whistling

sounds like whoever installed your intake may have not used a proper torque sequence and slightly warped the intake OR maybe you have an intake that came from the factory out of spec? .....which would explain both the base plate leak on with BOTH carburetors and the intake gasket leak.

I always bolt my intakes down from the center out in a criss crossing X- pattern.

you may find that even with a new intake gasket set that your intake is "sprung"