If you haven't already, you should check to see if you have rot or some kind of insect infestation. Around here, at least, they typically only go after wood with bugs inside.

Those fuckers woild pound on my gutters for hours. Never once on anything other than the aluminum gutters. But they love the loud hammering sound, as it calls out to potential mates. So when they find something loud they will tend to come back to it.

A couple years ago a wooden power pole (well specked with woodpecker drilled holes over the decades) in my backyard was replaced with a fiberglass one. At least one local woodpecker hasn't realized the futility of hammering on it to the tune of honestly almost cartoonish hollow BONK BONK BONK sounds, and continues to try to find a meal in the thing.

I feel bad for the bird at this point.

Not unusual... I have two metal towers running through the back third of my property. The flickers love to bang on them, it really amplifies the sound. I assumed it was more a mating/attention thing.

Yeah I think they're hammering on some component of my metal roof as it has a very metallic sound. I love birds in general but have considered loading my 22 with bird shot on multiple occasions when they wake me out of a deep sleep.