Presumably then that's what we're seeing, but if so it's extremely inconsiderate to be doing it at night. Is there no local/area government office you can approach?

In contrast, I (in my former life as a night shift supervisor/manager) have been on the other side of such issues, but always took noise complaints very seriously, as an enforcement notice could have had all sorts of repercussions. Didn't stop the odd vexatious complainer though. "I can't understand how a factory was allowed to be built in a residential area," which brought a wry smile as that particular block of houses had been built on what used to be the factory car park.