Neighbor finds the air-to-water heat pump too loud

you just have to know whether the "problem" is to be found within yourself or rather with the other person. The moment you say "ok, we can take a look at the problem with my heat pump" you have admitted your guilt with 99% of people

Sonic events (actual sound and overtones) propagate and are therefore never absolute, but are perceived differently at different positions (which I only refer to real effects, not to imaginations of future exes of the neighbors). The event can thus become a problem both at the source and at the "mouth" as well as on the way in between. It seems to me fundamentally – independent of the intellect of the other person – to make sense first to perceive problems and to make their elimination a joint endeavor. A peaceful coexistence has three components: 1. You, 2. Me and 3. the "and" in between. There are stupid people, probably nowhere as a critically endangered minority, but that should not influence any maxims.

It seems to me fundamentally – that is, regardless of the intellectual capacity of the other person – sensible to first perceive problems and to make their resolution a joint endeavor. A peaceful coexistence has three components: 1. You, 2. Me, and 3. the "and" in between.

Well described. To first accuse the neighbor of something is "Trumpism" in its initial stage. That it is only noticed now can be due not only to the change in technology (wear, defect), but also to the change in the use of the house (setting up a home office in a room that was previously little used).

So I can say the neighbor is not all there anymore. As others have already written, I told the neighbor that I had turned off the heat pump once and he said yes, it didn't hum either, although the heat pump was still on. He has also only been complaining since last summer, since he saw the device. Since we are planting a hedge behind the house anyway, so that the neighbors can no longer stare onto the property, there should be peace then. By the way, he is the only neighbor from the apartment building who hears it, all the others don't even hear anything at all.

That's already an important insight and it happens quite often. There are many similar examples from other fields as well ... Go ahead and drop a brochure of a psychosomatic clinic into his mailbox :)

Well, I can say the neighbor isn't all there anymore. As others have already written, I told the neighbor that I had turned off the heat pump once, and he said yeah, it didn’t even buzz, although the heat pump was still running. He’s only been complaining since last summer, ever since he saw the device.
Since we’re planting a hedge behind the house anyway so the neighbors can’t gawk onto the property anymore, there should be peace then. By the way, he’s the only neighbor from the apartment building who hears it; all the others don’t even hear anything remotely.

very very cool! you made my day!!

it’s like my neighbor’s ex! as soon as she was gone, the pump was no longer an issue^^

did you ever reveal it or tell him that it was on^^

I wouldn't tell the neighbor that directly... but would notify him once or twice more that you had turned off the pump again. If he then nods each time and says... yes, he noticed, I would go to him after the third time or so about an hour after he has nodded and say... your partner just told you that she turned the pump back on that day as well because she didn't know you were running a test ;) ;).