Why would a woodpecker peck the metal roof on the woodshed? Is he slow? He does this every year. Sounds like a machine gun in the backyard. I gotta imagine he's looking for love, why else does a guy do all that work?
It might be his call sign. The noisiest gets the most attention from the women. Aren't you lucky to have him in your neighbour!
I had the same thing happen. A woodpecker would peck on our metal rain spout early in the morning for a couple of years in a row! It would scare the chit out of us! Finally after a couple of years it never happened again. I wondered myself why he did that?
In one of the places I hunt I've heard them thumping on the big metal power line towers. Talk about loud!
Is it a woodpecker or flicker? Flickers are notorious for pecking on metal; roofs, stove pipes etc. Regardless which, he's either telling the rest of his kind this is his territory, or he's looking for a mate.