Ok I have found a new 'strange' noise with the 2tb Xbox One S.
It's the harddrive CHIRP
Those who upgraded their PS4 internal drives to seagate 2tb will know about this noise. It's a random and occasional Beep or CHIRP that the drive gives off.
It actually causes no harm whatsoever but it is alarming first time you hear it.
It only seems to affect 2tb drives and up to now only affected PS4's.
However my 2tb Xbox One S (limited 2tb versions on its launch replaced with 1tb & 500gb models) also gives off the same occasional random CHIRP
So if you do have 2tb in either your PS4 or Xbox One S - expect the odd CHIRP and don't be alarmed nothing bad is happening. It's just a freaky anomaly with those drives.