Think of an engine as being an air pump. A car with a free flowing exhaust will likely have less carb noise. The restrictive exhaust causes the fuel and air to resonate longer in the intake tract. I've seen the Diplomat/Gran Fury cop cars... 2 pre-catalytic converters, a y pipe into a single pipe, ANOTHER cat, then a muffler. Certainly NOT a free flowing system by any measure. Another reason... The Quadrajet is a spread bore carburetor with secondaries LARGER than the Holley. If you tried each carb on the same motor, the Q-jet would make more noise.
Finally, the cam timing in the crate motor is surely more aggressive than the cop spec 318. That will affect things too.
I have a cold air kit in my 2007 ram with the HEMI. It ROARS compared to the stock setup. If I ran it without catalytic converters, it would certainly be quieter.