I can understand how low frequency sound can be incredibly annoying. Oddly, some are soothing to me. There's this point when waking up where if I hear a gentle hum, it becomes comforting and I want to lay there and listen until it lulls me to sleep. There was something about the distant hum of the old Mack DSNY trucks, before the Volvo engine switch. I'd wake up to them but it was so nice to just lay in bed with that sound. I can also hear the MTA subway diesel engines on the elevated tracks a block from me. I also used to enjoy the sound of my mother vacuuming down stairs when I was a kid sleeping in on the weekend. At work I sometimes retreat to the pump room where the whine of machinery can be sort of soothing. I do have this ADHD anxiety thing and my head gets all swirly with things so the noise helps.
Sometimes I use a white noise sleep app and combine a few machine sounds into a sort of whining whirr of machinery. And I put it on low as if I'm sleeping in a room off down the hall from a machinery room.
Though sometimes it can be too much. Sometimes you just want to turn the sound off. I do hear a hum at night in my south Queens NYC neighborhood. Always begins around 9PM. I can't explain it but it's like a buzzing whirr that pulsates or whines a few times and then dies out in an echoey fashion. Then comes back minutes later. Often with large gaps between them. I could even describe it as almost like some alien spacecraft engine whine from a sci fi flick. They don't bother me a lot but if it became constant, I don't think I could sleep as its very low and shrill. I am near JFK and major roads so who knows.