Can any conclusions about aerodynamic efficiency be drawn on the basis of fly-by noise?
Invariably, aerodynamic efficiency improves with newer designs and so it was from 747-200/300 (not glass cockpit) to 747-400 (winglets + increased span + glass cockpit) to B777 to B787, from A300 to A350. Industry wide pilots were never disappointed by this and proud to be flying the latest lowest drag 'slippery' airplane.
But using noise as an indication of aerodynamic efficiency, could have peculiar factors come into play. The ultra quiet and ultra efficient B787 is so 'clean' or 'slippery' that it requires great anticipation and confidence in technique to fly both the 'speed control' and the CDA Continuous Descent Approach as published at some very major airports.
Many a time, it cannot be flown without the use of speed brakes, the use of which, is (was?) anathema for many pilots.
The  normal expectation is that as long as the speed is above the selected or target speed with speed brakes deployed to aid in reducing the speed, and especially during descent/ the engines would be at flight-idle. Contrary to this, a design feature of the autoflight system pushes the thrust levers up so that they are not at idle but producing thrust when the pilot is doing her best to make the airplane decelerate! So, earlier generation airplanes would have thrust at idle at these points, but the 787 does not.
Even under these circumstances it probably has a smaller noise footprint but an inability to decelerate as per the ATC published speed control targets, could for eg result in gear being lowered earlier than the published preference and this all adds to the sound. The Gear extension point is actually being monitored for variations at such airports.
Despite the above information, theoretically, aerodynamic efficiency could certainly be gauged on the basis of noise provided you were to compare like to like - the comparison would have to be between aircraft similar category, all the airplanes would have to be doing the same maneuver in equivalent configuration eg.

passing 500ft on final approach, max landing weight, landing config with gear down, on speed, and stabilised on approach

OR

level fly by in clean config, height 400ft, 270kts speed.

And there's no accounting for what factors, apart from aerodynamics and engines maybe discovered to be contributing to the noise level.