I live in a 3rd floor apartment, and I'm going to vent out a window that is about 20ft vertically and 20ft horizontally from a heavily trafficked walkway. I just bought a Can 8" HO 735cfm fan with a Can 75 filter. I haven't mounted them or run a ducting yet, but I turned it on just to hear it. Man, its pretty loud. I know I can reduce the noise with bungees and insulated ducting, and I really like that mounting box, but I'm worried about the sound of the airflow itself tipping people off. Does anyone have a similar sized setup? What does it sound like when you are outside in the vicinity of the vent? Should I get a muffler? I asked the owner of the hydro shop for one, but he said I didn't need it, even though he had them in stock. I figured he wouldn't pass on selling it to me unless I really didn't need it. Would a muffler reduce the noise of the airflow? What do you guys think? Please tell me something to ease my mind.