Wow, lots to unpack. Not in any particular order. I'll start with the simplest. Fences between neighbors have raised hairs for ions. Judges don't want to hear it. If you went to court, with all the plot plans and county docs and land surveyor specs either of you could muster, the judge would stop you both in five minutes, no matter how the fence sits, and make you each pay half. 99 times out of 100.
I'm flattered that you even bothered to read my post. I probably wrote it late at night, and I do go on. Like most of my musings, and as I have admitted here countless times, most of my thoughts are projection. How I would feel. What I would think. Or how I think others should think. All worth barely a grain of salt! But even if I was dead wrong, if I contributed in even the tinest way to bettering your relationship with your neighbor, I'd be pretty proud of that. And you showing him the post! Well that was unexpected!! I might have written it differently had I known he'd be in the audience!
I had a little trouble following along with who said what in the convo, but you certainly gave him every opportunity to express himself, and that's amazing. For whatever it's worth, I'd be happy to have you as a neighbor! You know, as long as you get rid of that d--m pump!

And if I read it right, and it's this same neighbor that has a dog that barks at you, I take it all back, all bets are off on the pump noise! Tit for tat. Heh, heh, heh.
For the record, my pronouns are still the same ones I was born with: he and him, but I appreciate you giving them a thought. Ha, I thought one of our members was a woman, based on her avatar, and I referred to "her" as such for years. He finally sent me a PM and corrected me. Turns out the avatar was just a pic he liked, "she" wasn't him at all! He thought it funny, and didn't say anything for all that time. But then he changed his avatar to a hot rod car. Ah, the world in which we live. Whaddayagonnado?
And you must know, and I acknowledge, that I couldn't possibly have known with any certainty that what I was guessing at, or "guaranteeing" was 100% true. It was all conjecture, and only intended to give you something to think about.
It honestly sounds like you are trying to do what is right for your neighborhood. Even
thinking about your pump volume, and being willing to discuss it here, and directly with your neighbor, puts you in the top 98% of good neighbors. Many wouldn't even be aware of it, and others would know it was loud and wouldn't care (the "tough noogies" crowd). So kudos. I have no doubt you'll address it as best you can, when you can.
I can explain the bit about "you should not rely on the kind nature of your neighbor for a solution (as you have been)," like this. It was mostly more projection, but I could make a case that you did
imply that you are doing that (even if you're not aware you are). Merely by the fact that you know the pump
might be bothering him, but are waiting for him to
complain about it before
doing anything about it. That's what I meant by relying on his kind nature. Still, I was only guessing that it might actually apply to your situation.
My [round-about] thought process: I have extensive yard lighting. I made a point to have direct conversations with all the surrounding neighbors that might get even a glimpse of my lighting to make sure it was not bothering them. I didn't have to do that. I was applying the golden rule. "Can you see my lights? Are any shining in your windows? Should I re-aim any of them?" I was trying to convey several things, some neighborly, some self-serving. I wanted them to think that I was a decent, respectful neighbor, who would go out of his way to make sure nothing I was doing in my yard was bothering them (golden rule). Whoopie for me. But I was also hoping to send the message that I would sure appreciate they treat me and my home with the same respect. Sort of an ad hoc boundary-setting/rule-making dealio. Is that the definition of passive-aggressive? I dunno.
Do I expect them to adhere to my made-up code? Expect? No. Wish?
Yes. They know their dog barks. They hear me quieting him. Which means I think they should assume it bothers me some amount. They should also know, because of the yard lighting convo, that I am the kind of guy that feels people should not be unreasonably bothering their neighbors with what is going on in their own yard. And see? I'm
still projecting, assuming others should put all this together like I would. Regardless, there's not much they can do about it now. They picked the wrong breed for our neighborhood lot size (a border collie), and now they are stuck with him. So (even
more projecting), I imagine that they are relying/imposing on my good nature to solve this problem for them. They have to choose between bothering me, or disappointing their three kids. No contest, I lose (and I wouldn't want to disappoint their kids either). And I'm not going to blow up my relationship with them, or their kids, over the few times I have to deal with their dog. Do I actually think they've thought about
any of this? Who knows. I could imagine your neighbor feeling something similar. Does he wish he couldn't hear your pump? Why wouldn't he? But he knows you have a pool, and they need pumps, so he's made up his mind to ignore it, and that's that.
So... it seems neither of us can say for sure if your pump is actually bothering your neighbor or not. I would still argue, given his line "I've been listening to that pump for 19 years, doesn't bother me a bit," that the first half of that sentence is more telling than the second. Technically, you only have to take that line at face value. You did your due diligence. More than most neighbors would.
But no matter, my previous final thought still stands: even if it's not bothering him, you'll be happier with a VS pump, it'll save you money, and you can pretend you got it just for him, and maybe get some points for that (See? Ultimately, I'm self-serving!). So even if he still thinks you should pay for his half of the fence, maybe he'll see the new pump as some just compensation. People can rationalize just about anything, right?
Anywho, thanks for hearing me out, whether it helped solve anything or not!