The hallway on the second story of my house is quite narrow. Not even two people wide. I was home alone, and walking through the hall. With no waning, I hear an EXTREMELY loud pop from my right side. But there was only a wall on that side. And it sounded as if it came from RIGHT about my shoulder. Like someone fired a gun next to my ear. I was so startled, I leaped down a flight of stairs accidentally slammed my face on the wall. Hasn't happened since, so maybe the spirits feel bad.