shall we assume that the anecdotal testing at apple and BIL's house was after being exposed to your home electrical environment?
That's an interesting observation. Admittedly one could argue it's, at minimum, a nuisance variable, but that position has a few holes in it. You know the old saying about the word assume, and the one about correlation & causation. From an investigative research standpoint it might be advisable to look more closely at other variables and hypotheses in this endeavor. Example: Aside from those four, the rest of the whining Studios were never exposed to his "electrical environment." His 9 plus other Macs were. They did not complain (whine about it). Add another variable, rinse and repeat.
As for the subject post, it's actually less anecdotal than the vast majority of content on this, or almost any other non-academic or research, etc. oriented forum. His other Macs did not present such a (2.2 to 2.6ish KHz.) noise. No known electrical problems in his home. Same noise occurs at a relative's house and, at an Apple store, an arguably more "rigid" test environment. I would not call that last one objective though. If anything, it's biased
against finding an issue. Now, add in the fact that he's had three replacements. That alone says a lot.
At some point, if your complaints have no merit, or you're up to a scam/con-like behavior, or otherwise abusing the right to return, you'll eventually get a firm no. He didn't (x3). So, he's either a very good lawyer, or did something really bad and it's karma (insert joke about being redundant), or, he's a legit customer who had a recurrent problem, and Apple knows that they have one too, however large/small, serious/minor, etc., it may be.