I have been hearing that same noise at the same time, but I live further inland, almost a mile up 54th from Superior St. At this distance, I assumed it was a train. They often move freight cars up and down those tracks late at night and I was thinking that was what I was hearing. If you are closer to the tracks and don't think it is a train, then it must be something else. I have heard the noise a lot lately, so whatever it is seems to be on some sort of schedule.