Does this sound normal?

The passenger side manifold is not an early hipo manifold. Don't know about the driver's side. Didn't see a flapper on manifold but there might be one there, don't know.

I've had some carbs make a loud sucking sound when they had an internal problem that was causing them to pull fuel through the venturies at idle. Easy way to tell if this is your problem is to (very carefully, best way is to use a mirror) look down the throat of the carb while the engin is idling. If fuel is dripping or running from a booster venturi there's a problem.