AR: Exactly, I think the bat is a lot more likely source for the sound than a metal grate (Does the metal grate set in a metal frame or on concrete?). It seems more likely to me that someone threw the bat expecting it to land on the ground near the house. The moon was on the opposite side of the house and low in the sky, there were several trees and bushes on that side of the house...I don't think the perp expected it to hit concrete....was moving fast out the door and headed toward the alley.

On the other hand, I would expect someone entering or leaving thru the metal grate to be deliberate and careful not to make any noise....I wouldn't expect them to just drop the grate into place carelessly. Besides, I don't think this was a heavy cast iron grate (at least it doesn't appear to be) but a series of metal bars held together with metal rods. It would be much more manageable than a cast iron grate-not likely to get away from someone.