Noise issue in apartment (looking for advice)

So, last night at around 8:30 PM an extremely loud, unabated rattling started from my neighbors apartment. I'm assuming it's their air con on their last legs, or something like that.

It's so loud, that I had to pull out my old futon and sleep in my entry hallway, with another pillow pulled over my ear. Even then I could still hear the sound clearly.

At around 3:00 AM I couldn't take it, and tried knocking on their door/ringing their bell a few times, though they didn't answer. From the balcony, I could see their lights were on, and their apartment seemed quite messy. It may not be related, but I was looking for any way to find the source or notify my neighbor.

Noise was still going strong (maybe stronger) this morning when I left for work. I only got about 2-3 hours of sleep. I won't be able to stay in my apartment for very long if this continues when I get home today.

As such, I'm looking for advice on how to proceed. This isn't your typical loud footsteps/talking late at night. It's constant, and feels like torture.

by ConsiderationMuted95