Sound travels in straight lines - air turbulence creates noise
So you want to avoid a straight path for the air to follow and you want the flow-path to be very smooth.
First: did they do a heat load calculation to determine that you actually need 2 tons of cooling and the aproximately 800 cubic feet of air flow for it?
Next: did they test to prove that you are getting the correct airflow? Or did they just set the blower for "the highest speed for cooling" and run out the door with the check? <g>
After the above two questions are answered correctly, and if you can tolerate the loss of space, a blank, well overlapping 'baffle plate' can be spaced out from the wall to cover the return opening.
Or two sets of 45 degree vanes could be installed internally in the air return path.
PHM
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When faced with the choice between changing one's mind, and proving that there is no need to do so, most tend to get busy on the proof.