The OH 6 not modified is very quiet , with the wind at my face had a few sneak up on me. 20 feet no hear
(I had an old crappy OH 58)
The quiet one is the quietist #1. low gross weight, larger TR with extra blades, muffler and sound blankets ..
The Special project MH 60 with the airframe mods and tail rotor is stealthy IR & Radar cross-section works but the higher gross weight & power output = more noise
( sounds like a smaller helicopter further away )
Still good in anyones book