1. The sound is attributed to trees cracking
2. The cracking is caused by sap freezing and expanding
3. Sap freezing produces sound in the ultrasonic range
4. So it's not the trees
Point 4 is not a valid conclusion from 1-3, because it was never stated that the sap freezing is what is being heard. Rather, it's the trees cracking, which is _caused_ by the sap freezing... but its own thing with its own sound.
> This sound is often attributed to X. But <some component of X> doesn't make sound that humans can here.
The "people say it's this, but actually ..." reads, to me, like they're saying it's _not_ this. Which was point 4.
> scientists have found no evidence this phenomenon might make sounds that are audible to the human ear.
Which I take to mean they’ve measured ultrasounds but no audible sounds.
To me, your reply actually highlights what I was talking about; because your use of "this phenomenon" is _somewhat_ ambiguous.
1. "this phenomenon" can be the sound of "large pressure splits in tree trunks, caused by sap freezing and expanding" (presumably audible to humans)
2. "this phenomenon" can be the sound of "freezing sap in trees" (presumably not audible to humans)
For that to have not been the case, either they would've had to freeze sap in the lab, or they would've had to go way out of their way to isolate recordings of just the sap in the field without the rest of the tree (is that even possible with normal recording tech?)