bdft
CGN Ultra frequent flyer
I have worked around and under many big American and Russian helicopters. While I wouldn't call it "whisper mode" even the Mi-26 sounds relatively quiet when its working close to the ground at a distance. They seem to have an odd low pitched whistling sound that is hard to locate until they come over the ridge line and then it's a different story. The Chinooks and Skycranes are all noise all the time.