I didn't think much of it until a few days later... Someone knocked on the door, but since I was recently out of the hot tub and drying off in the house, Kirsten answered it. Turns out it was the landlord for the people who live in the house behind us. One of his tennants apparently complained about the noise of the hot tub filter. Kirsten didn't get the name of the tennant however, the contact information for the tennant, the contact information for the landlord, etc. She did, however, badger and grouse about the issue repeatedly. I spent an hour or so researching the law regarding the matter, and it seemed pretty clear cut for Santa Clara -- I am allowed to generate noises up to 55 decibels at our property line in this town at night, which is reasonable. 55 decibels being the approximate volume of human speech.
The hot tub was running and Kirsten was outside, so I explained this to her, walking her over to the border for our back yard, where you could hear the wind, the windchimes, planes overhead, street noise... and, just barely, a slight hum from our hot tub filter, no noisier than a whisper.
"You know how I said that we can only be up to 55 decibels?" I explained, "Well, a person talking is about 55 decibels, and which is louder right now? Me talking, or the hot tub?"
She admitted that she could hardly hear the hot tub in comparison to speech, but proceeded to worry more about the whole situation, wanting to limit usage of the hot tub after 10pm, and other various things that I could accept if we were talking about the use of a shared a hot tub in an apartment complex with neighbors, but which made no sense given that we're paying for a private house with fences on the property line, etc. We only have to meet our 55 dBs at the property line obligation and that's it. The fence between us and the neighbor, combined with their house should be plenty to keep the noise out.
Turns out that the snooping neighbor from hell actually complained to the city before they had their landlord talk to us, so Kirsten called me up today to let me know about the letter. Then she called me up a second time. And then a third. All in the course of about an hour... then she went home and fretted a bit more. I feel like I'm being treated like Basil Fawlty today, except that unlike Basil Fawlty, I'm neither rude nor incompetent. If she doesn't stop pestering me, I'm sicking the fire ants on her...
Meanwhile, when I wasn't running for the kitchen phone today, I was outside, trying to determine what I can reasonably (i.e. affordably) do to reduce the volume level further. I drained the hot tub completely of 350 gallons or so of water (what a waste!) and slid a large sheet of leftover kitchen flooring under the section of the hot tub that contained the pumps, thereby insulating some of the noise and vibrations that might be radiated into the wood of the deck. I refilled the tub completely... and, after all that, it's marginally quieter. Marginally...
Right now, I'm in the computer room, which is maybe 7 feet away from the hot tub which is directly outside the window. The noise of the hot tub is no louder than the noise my computer is making, and since the deck is directly against the wall of our house, there's no way that the neighbor could get nearly as much sound from the hot tub in their place.
I contacted the City of Santa Clara and talked to their guy, who seemed pretty reasonable. He scheduled an inspection on Monday the 23rd. I'm really looking forward to the results, because we are **so** going to ace it. As for as the neighbor across the way, I'm thinking it would be a great idea to hold a late-night "noise abatement" party sometime in the near future! ;->