I pointed into the air. It’s still there, I said. He sighed and shook his head, but we both listened, this time for ten whole seconds, scanning the room with our eyes.

I don’t hear anything, he said eventually.

It’s almost like a vibration, I said.

Paul asked if I left the hood vent on in the kitchen. I couldn’t rule it out. I groaned, peeled myself from bed, and pulled on the nightgown I’d left bunched on the floor. I trundled out into the hall, passed Ashley’s room, and descended the stairs into the darkness of the ground floor, where a constellation of red and green LED lights signified security alarms, fire detectors, carbon monoxide detectors, Wi-Fi, thermostat controls, all of the systems animating the body of our house, unnoticed and unappreciated like breathing or circulation. I entered the kitchen and listened. The hood vent was off. The fridge sounded normal. But the hum was still there, just as loud as it had been in the bedroom.

I walked into the dining room, and again, the sound remained unchanged, which I found unnerving. I wondered if I was suffering from some sort of tinnitus. I raised my hands and pressed them over my ears, and the sound was dampened. It wasn’t in my head. The sound was coming from somewhere. I stood in the dark beside the table, where the plates from dinner were still piled, abandoned until the sobriety of morning, and I began to turn my head slowly, hoping to detect some variation in volume or direction. I then began to pace around the room. The moment I felt certain the sound was coming from one direction, and moved towards it, it suddenly seemed like it was coming from directly the opposite direction, behind me. I wondered if it might be our neighbour Farhad working with a power tool in his garage; he’s been known to mow his grass at ten o’clock at night. But that noise would have a clear direction. Whatever this was seemed completely diffuse.

Ashley? I called upstairs. I waited for a reply, then walked into the front hall, to the foot of the staircase. Ashley?

Yeah, she shouted down from her room.

Can you check—? Did someone leave the bathroom fan on up there?

There was a pause, and then the sound of her door opening. She appeared at the top of the stairs in plaid boxer shorts and a baggy white t-shirt, scratching her scalp through her post-gender haircut. Ashley once said her spirit animal was Sinéad O’Connor, circa ripping up the photo of the Pope on Saturday Night Live.

What? she asked.

The bathroom fan. Did you leave it on up there?