Well, I have determined the source of the alarming noise.
Actually, there might be 2 sources because:
1. When we went outside the evening of the incident, we realized that one of the gutters had fallen off the house.
2. When I got into the shower later the day of the incident, I saw that 3 tiles had fallen from the shower wall into the tub.
Some might find this a relief. I find it alarming that, in spite of shockingly loud noises mere feet from our bed, 2 dogs, 1 cat, and a husband slept through the whole thing. Which means that, clearly, someone could come in and murder us in our beds.
Plus, let's be honest, I'm halfway convinced a ghost is responsible for both the gutter and the tile.