The hum doesn’t stop. That’s the whole complaint.

The sources of the sound are cooling and power: chiller and fan banks running around the clock, transformers, and, at sites generating their own power, gas turbines. Typical readings near facilities run 60 to 80 dBA at property lines, with diesel generator tests reaching 80 to 100+. Three properties make the experience worse than the numbers suggest. The sound never stops, and chronic exposure is what the health literature studies. The sound is tonal — a hum at a specific pitch reads as louder and more intrusive than broadband noise at the same meter reading. And much of the energy sits below 100 Hz, where sound travels farthest, penetrates walls best, and registers weakest on the A-weighted meters most ordinances specify.

The health baseline comes from the WHO’s environmental noise guidelines: chronic exposure links to sleep disturbance, annoyance, and cardiovascular and metabolic effects, with roughly 16,600 premature deaths a year in Europe attributed to transport noise. Read that citation carefully: the WHO studied traffic and aircraft, not data centers. What the guidelines treat as most intrusive at night, though, is precisely the continuous tonal pattern data centers produce, and a 2026 review of low-frequency noise around data centers is the literature’s first attempt to close that gap directly.

Mount Pleasant, Wisconsin.The $7.3B facility Microsoft calls its most powerful AI data center drew a federal class action in July 2026: cooling and generator sound allegedly audible a mile and a half out, on behalf of more than a thousand households. Microsoft’s own April community update had already acknowledged a “tonal humming sound” reaching residents to the north: an operator conceding the phenomenon while the litigation argues its extent.

Vineland, New Jersey. Residents describe loud industrial noise around the clock near the DataOne facility, the same site whose unpermitted generators anchor the enforcement guide. The county health department measured, found the state’s 50 dB nighttime limit exceeded, and issued a violation notice in March 2026; a class action followed in May.

Dowagiac, Michigan. A site that ran as a crypto mine from 2021 converted to AI computing in 2024, and the continuous cooling made the noise worse. Residents compare the sound to a vacuum cleaner running in the living room. The city passed an industrial noise ordinance and issued fines; the operator is contesting the measurements; the CEO publicly offered to buy the neighboring homes if mitigation fails; a class action arrived in May 2026. One site, the full arc, still unresolved.

Loudoun County, Virginia.In the densest data center cluster on earth, a news crew’s meter read 90 dB at one facility, and residents near another, which runs eight gas turbines continuously, kept complaining while official measurements came in below the county’s violation limit. The county’s response was to form a working group to review the ordinance itself, which is what a code admitting its criteria miss the problem looks like in procedural form.

One labeling rule this page enforces on itself: Granbury, Texas is a crypto-mining facility, and also the most heavily litigated noise site in the country, with four legal actions, health documentation, and a failed attempt to incorporate a town solely to gain noise-ordinance power. The acoustics and the law generalize to any 24/7 computing load; the workload attribution does not, and borrowing the case for AI without the label would be exactly the drift this series exists to catch.

The instructive case is Great Oak, in Prince William County. A 291-home community reported around-the-clock cooling noise from Amazon’s adjacent data centers, with sleep loss and migraines in the record. The county’s ordinance, written in 1989, exempted commercial HVAC noise, so for years there was no violation to find, because the code had defined the noise out of existence. The county removed the exemption in March 2023 and later adopted continuous-noise limits. Then came the two twists that make the case a syllabus: the roughly $40M fan replacement lowered the pitch of the sound, after which residents reported rattling picture frames. The mitigation moved the energy down the spectrum rather than removing it. And the new rules grandfather existing equipment, so the community that forced the reform may never benefit from the reform.

Chandler, Arizona is the complete arc. Residents logged over a hundred reports of a high-pitched chiller hum beginning in 2017; three hundred signed a petition. Without litigation, CyrusOne retrofitted sound attenuation onto every chiller by October 2018 and committed to factory-attenuated units going forward; residents reported roughly 60% improvement. The city then wrote sound mitigation into a 2023 ordinance, and in December 2025 its council rejected a proposed AI data center outright. Complaint, retrofit, code, and finally a siting consequence.

New Albany, Ohio is the operator-side counterexample this page carries deliberately: after resident feedback about exhaust fans near Google’s campus, the company had a sound engineer engaged within two weeks and implemented monitoring and dampening. The city’s own FAQ reports four operational-noise complaints in fifteen-plus years of data center development. A city with an interest in saying so, saying so; the tier label on the citation does the disclosure. The point survives the source: outcomes vary enormously by operator and by code, which means neither “always a nightmare” nor “never a problem” survives contact with the record.

And the highest-leverage community move on the record is a measurement: the Prince William coalition commissioned a professional acoustics study, one of the only independent, methodical measurements of data center noise at residential receivers in the public record. Every argument after that study had a number the record was required to carry.