Air conditioning noise
A/C noise is not a ducting problem.
It is caused by taking an ac unit that is to small and run it at aircraft propeller speeds trying to get proper cooling.
Think about it / build the A/C unit a little larger, slow the fan down, problem solved.
Ducted A/C does not work well in extreme heat areas, sun overheats the roof and kills the A/C.
35 yrs in the A/C business.