Earlier quoted context omitted.
According to the article, the drumming sound they make is for communication; pecking to find food is relatively quiet. He's drumming on the metal chimney cap because it's the loudest thing he can find.
But what’s he saying? What’s in that tiny bird brain worth going on about at 4am? Cats? Smoke? Food? Bird problems, amirighht?
The hammering is how they find eachother over long distances. Just heard some the other day hammering on my gutter. Went out to scare him off, and lo and behold there were two pairs outside frolicking around in the trees.
A couple years ago I saw one while I was out on my back deck, he started hammering, then about 2 minutes later a female shows up, and they flew off together.