I just tried turning the noise cancelling on on a pair of mine while they were not connected and while I was in a quiet room environment. I can definitely hear a static noise, but I wouldn’t say it’s as loud as running tap water. Strangely enough, I never heard it while in the plane - on the ground with the engines shut down or while flying. Sometimes I can hear noise, but it’s coming from another pilot’s microphone, because once I turn the interphone off, it’s gone. I’m using full volume on my headphones and control the volume through the audio control panel.