Thanks for the info Eddie.
It's not the fan as that shuts off after boot.
The heat pipes. What noise would they make? Noises when they change temperature?
Does not sound like metallic noises due to temperature changes.
Sounds more like some sort of "data flow" for lack of a better description.
Maybe it's the SSD? Maybe that's in more or less constant use between the S6 software and the Windows shell?
Are there different hardware revisions of the MTM?
Any changes over the years that could affect this noise issue?
Here's a better recording of the noise:
https://www.dropbox.com/s/yux010kun4...2%205.m4a?dl=0
Do you hear that on your S6s? Quite audible within a foot or two from the MTM.