clean air intake and also unrestricted air exhaust. With a real muffler you might be able to also pipe the exhaust outside the enclosure.
Also, if you offer to supply their electricity I doubt they will complain. I also seriously doubt that any police officer would enforce the noise ordinance in an emergency situation. I don't recall any writeups here in Springfield last year during the ice storm and many had their generators running 24/7 until electricity was restored.
Mike D.