In my old place i ised the grow weed easy dot com stealth exaust window board with blinds over the black painted styrophome sheet and the window cracked some.
Scroll down to stealth exhaust:
Give your cannabis plants just the right amount of breeze indoors, and learn how to easily make a cheap, stealthy exhaust system...
www.growweedeasy.com
For noise a short run of straight flexible duct to long or curved is louder. And a duct muffler last before the window exhaust.
Looked like a dark room with a desk fan or something going from right outside the window.
No one noticed and it was a trailer park with the next trailor 30 feet away from the window and the neighbor cuttting the lawn right up to our house.