The Zoo over Ambuscade Street

I didn't go to bed until after midnight. I woke up at 4AM, and couldn't go back to sleep because of the Thumping Noise of Doom. I haven't been able to identify what's making this noise, but it only happens at night when it's really quiet, and it stops as soon as I leave the bedroom. It's coming from either the kitchen or the floor underneath the kitchen, and sounds like someone knocking on the cabinets. It's driving me insane!

And, truthfully, I'm really worried about it, because I don't know what's making it. It probably means there's a problem of some sort, but I don't know what. Or what to do about it. Or even how to find out what it is.