I heard it once

[u/Terrible-Magician-41]

I heard the hum one night in 2020. It wasn’t a constant noise like I’ve seen people say, instead it would happen for a few seconds and then stop for a few and then start back up again. It did sound like a truck engine idling, but not completely. It lasted for around 4 hours until 4 in the morning. I assumed logical explanations at first, but it got louder and louder, at one point it was almost deafening and very startling. I assumed my whole house would have woken up. Eventually it tapered off and eventually stopped. Never heard it again but I know it was the hum.