People assume a data center hums because thousands of computers are running inside it. Almost none of the sound reaching the neighborhood comes from the computers. A GB300 NVL72 rack draws about 140 kW. Essentially all of it leaves the building as heat. Amazon’s campus on Tanner Way runs more than 400 rooftop exhaust fans, about 600 feet from the houses in Great Oak. Prince William County allows 55 dBA at night at a residential property line, and campuses are designed to come in under it. But here’s the catch: Fans and transformers make low-frequency tones. Low frequencies travel farther and go through walls. Counties measure in dBA, a scale that barely counts the low end. A 73 Hz hum reads about 24 dB quieter than it is. So a site can pass its noise limit while the people next to it still can’t sleep at night. How to fix this? Distance. Sound drops about 6 dB every time you double it. Low-frequency rumble carries farther than that. Enclosures and silencers. At xAI’s power plant in Southaven, Mississippi, a $7M sound wall went up last December, and the company promised a $12.8M earth berm as well, to screen the gas turbines. Slower fans. The fans have to get rid of the heat, you can’t just turn them down. Amazon put new motors and better blades on all 424 exhaust units at Great Oak, made the stacks 3 feet taller and rewrote the controls to run the fans slower and in sync. That cut the noise by about 10 dB, and the fans use less power doing it. It was a four-month retrofit of every fan on the roof. Amazon has never said what it spent.