I did a quick recording last night, using voice memos on my iPhone, and here's a spectral graph of the audio file. Around halfway, you can see the lines intensify, and that's when I moved the phone a few inches above and behind the Mac Studio (edit: from approximately where my head is when sitting in my chair).
When I select and listen to ranges of frequencies, that lower frequency stuff is the whoosh of the fans, and it sounds fine (maybe even soothing). But, those lines showing pretty much continuous tones are the problem. This matches the 2.2 KHz shown in other graphs, and there are lines at about 1.5k and 2.7k, too.
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