Only thing I can think of would be putting baffles in the opening so the air has to change direction several times. Each change in direction, there'll be a reduction in sound level. I had something like this in a darkroom that only had 3 ply baffles painted flat black that worked well. For sound, I'd consider finding some sound deadening material, like gooey rubber coating or material such as cork, which should further dampen sound. I doubt you'll get rid of every sound, but likely bring it down to a livable level. If you want air flow, a squirrel cage blower should do the trick.
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