Lots of animals can hear and make infrasonic sounds. Some are even thought to be able to perceive infrasonic waves travelling through the Earth in the wake of natural disasters and use these waves as a kind of early warning system. Like the rats and snakes deserting the ancient Greek city of Helike, before it was devastated by an earthquake. Or the animals that fled the areas affected by the Indian Ocean tsunami, hours before disaster struck. I once read that some church organs can produce infrasonic bass notes that induce feelings of transcendence by increasing heart rates and releasing endorphins, causing congregants to tear up, shiver, or feel as if they’re communing with God. It wasn’t far off the effect the hum had on me, to be honest. The crying and shivering at least.

Once back in the car, I pulled out our map of the neighbourhood. Laying it across the dash, I placed a small yellow sticker over the pixelated aerial view of the industrial park and jotted down the measurements with a thin-tipped black marker. Red stickers would indicate sites producing sounds over a hundred hertz, yellow stickers would indicate sounds over fifty hertz, and green stickers would indicate sounds in the sweet spot—sounds which could be our hum. Hopefully a pattern, or hot spot, would slowly emerge. I folded away the map and shifted the car into drive as we set off towards our next site—the electrical substation on San Mateo Road.

I still think we should visit Harding, Kyle said, pulling out his vape from his pocket.

Hey, what did I say? Not in the car.

I thought it was fine if the window was down.

I bit the inside of my cheek. Sometimes he really tested my patience. I couldn’t stand the smell of his flavoured vape: a sickly sweet cherry, which reminded me of childhood cough syrup. The windows were automatic, so I turned the key in the ignition.

Who knows what kind of aircraft or low-frequency weapons they’re testing over there, he said, blowing a little aromatic cloud out the window.