I’ve assumed it was highway construction but then saw previous comments about scrap ships in the port. I didn’t think of that and I guess it makes sense — but wouldn’t it sound more like crashing noises? This sounds more like deep droning noises from where I am.

I noticed it at midnight and then again at two, as well as times in the past.

Nowhere near the same, but waking up to that sound reminds me of this part in War of the Worlds 😱https://youtu.be/xr10zBblEw0