I mostly agree with your point however IMO the psychopath thing is not a great example because it could be explained as the incomplete or nonexistent development of something that is complex that is beneficial. I think the error is that we can’t necessarily know what the cost was. And the benefit doesnt necessarily have to be that big relative to the cost. I mean I’m replying to you and that me costs something, and what’s the benefit?

While the sounds don’t make themselves, they could be a side effect of something else… instabilities in the structural tissue, the plant straining to increase the movement internal fluids… who knows?

That said, I personally think there is communication between plants, or that at the very least it’s something like trying to mimic predator insect sounds. But could be that the vibrations themselves help move fluids around (as opposed to being a byproduct of something else that does)