YouTuber called Sir Avalon from Netherlands had this to say on
YouTube comments section:
"i Found the problem. Its called Coil Whine (Coil Noise). Its a defecte coil on the mailboard (at the right lower corner under the heatsink).
On this Image on the top left, just right above the E.
It is resonating and reacts to processor load. This is why when you play a game the sound is changes or even is gone.
Fix is to put superglue on it, But then you will lose your warranty. (and is a hell of a job to do) if you have warranty, send it back to Microsoft."
I asked for more information...
"Hi! Thanks for the info about Xbox One noise issue. Could you tell more about your research. You opened the case and located the noise source? When did you buy your Xbox One? American or European model? Is the noise still there, if the Kinect is connected to the console? Are you 100% sure about this?"
...and he just responded:
"Hi, yep i opened up the housing. Thinking it was the HDD but then i discovered that the noise came from under the heatsink. Its an European model bought on sept 5 (releasedate of one in Holland). When i touch the coil with my fingers the sound is almost gone."