About ten years ago, I started hearing a low-frequency hum in the evening and at night. It was very noticeable and uncomfortable and often made it difficult for me to sleep. Earplugs didn’t work, so I started to listen to music or voice (audiobooks, interviews) to block it out to make it easier to sleep.
I started noticing patterns. The hum started late afternoons on weekdays and lasted until around 7 am, and it was on 24/7 on weekends and school holidays. I walked around the neighborhood to see if I could figure out where it came from. After a while, I honed in on a school about 300 meters away, especially as I noticed that their ventilation system was turned to a maximum at the same time I heard the hum at my house.
I contacted the principal of the school, explained the situation, and asked if they would consider turning down the ventilation system during off hours. She was kind and understanding and the hum went away for a couple of years.
Then it came back. I again contacted the principal, who now turned out to be someone different. This one outright dismissed any possibility of the ventilation system creating a sound that could be heard in the neighborhood, especially 300 meters away. I guess this person was not very familiar with the hum phenomenon and that large-building fans are one known culprit. So the hum continued and again made sleep difficult.
This went on until the school was shut down and demolished some time later.
The hum has been known for several decades, and people hear in different locations around the world. Often, people are stymied in trying to find the source. And sometimes, through some detective work, we can find the source and do something about it. (Or not, as was the case with the second principal.)
I thought I would share my story in case it can help someone, and it may be a piece in the bigger puzzle of the hum phenomenon.
Note: This was in Ski, Norway.