A summer alarm clock….when did they learn to knock on metal pipe ?

Our resident Yellow Bellied Sap Sucker is back for the summer. He will knock on any metal around the yard including the aluminum step ladder. He sure makes a noise ! And does it carry ! I’m sure you can hear him for miles

I have three questions. The first…. how and when did they learn to knock on metal instead of trees to announce their presence? The second…..How do they manage to keep their bills in good shape….that’s gotta hurt !! The third….Do they ever get a headache?