
Aircraft noise is normally measured in decibels by the techie types who do the research, then converted to phrases like "as loud as a pneumatic drill at fifteen paces during a hurricane" so the (mass, non-technical) media, politicians./+beancounters can "understand it" (even though most of them don't have a clue what a pnuematic drill at 15 paces in the middle of a huricane sounds like either - but it sounds as though they should).
I don't think Airwolf had a whisper mode, but Blue Thunder did. I think it is the only thing on there that didn't really fit in with their "every thing you see on this helicopter is already in service" guff... helmet-aimed weapons - check, spotlights capable of illuminating a suspect from several hundred feet - check, voice/systems recorders that kept track of everything the crew & heli did - check, fancy mikes and thermal imaging cameras capable of listening & watching through (thin, American) walls - check; whisper mode where you can hover outside a 1000ft skyscraper (presumably with double glazing!! - wonder why they couldn't hear the whiny little Astazou hanging outside their window..?) and spy on your local quasi-autonomous non-Governmental organisation preparing to tear down hundreds of years of civil freedoms and liberties - nope, that didn't seem to be around then.
But as anyone who watches 'Sky Cops' or similar programmes knows, the Boys (and Gals) in Blue can sit quite nicely several hundred feet up and still see you as clear as standing next to you...so you probably won't hear them anyway. So behave nicely to your fellow citizens and you should have little to fear...
Black helicopter? What else?