foxbat

That's because Samsung have sensibly included an internal cooling fan. It's extremely quiet but you can hear it if you put your ear to the back of the camera while it's on. I never knew it was there until I was filming in a totally silent forest and I could just hear a very, very quiet whirr out of the back of the camera. It wouldn't surprise me if the internal audio capture has a digital filter to remove that frequency from the audio tracks either.