I started hearing it several months ago, just once in a while, always late at night. There were strange loud noises at night. The chug chug of a diesel engine accompanied with strange whirring and grinding, electric humming and buzzing. Clanging, creaking.
What was odd was just how close it sounded. Like there was machinery running right outside the building, maybe even in the building somehow. My building is right near a commercial area. I just assumed one of these businesses was using trucks and heavy machinery at night, and that it sounded closer than it actually was. I had no idea how close to home, and how sinister and evil these sounds actually were until recently.