Well, woodpeckers peck for bugs to eat... not usually on houses, but could you have some ants? Termites? Perhaps you ought to have an exterminator look at the place.

Woodpeckers are designed to stroll up and down vertical tree trunks, they are quite capable of getting a grip on the siding.

Bugs in the siding are certainly one possible attractant.

Woodpeckers are territorial, like many other birds, but they don't have much of a singing voice to let other woodpeckers know of their presence. So instead they like to "drum" on any resonant surface that will make a loud noise and broadcast their message to other woodpeckers: "Keep away!!"

In nature they would choose a hollow tree for this, but yours have found that your home works just fine as a sounding board.

Unfortunately I'm not sure know how this information will be of any use to you in solving your problem.

You might try hanging up a cheap mirror in the area they are attacking. They will certainly mistake their own image for a rival. They will likely attack the mirror/image, for a while, but may be frightened off when the "rival" refuses to budge. [Of course they might be inspired into a frenzy of drumming instead, heh.]

The web link below may have some useful info.

Here is a link that might be useful: Woodpecker info

Have you noticed bees around? We had a problem with woodpeckers going after our cedar house. They were trying to get the carpenter bees that were drilling into our cedar siding & making nests. Talk about awful!! We had 3/4 round holes from the bees & then long gashes from where the woodpeckers tried to get them. Finally we had an exterminator come out & spray for the bees. They quit coming & so did the woodpeckers. Bad thing is the bees are seasonal- show up about March & stay til about August.

I had a woodpecker try to build a nest in my house. He enlarged a knothole and pulled out some insulation. I thought it was kind of neat sharing my house with a wood pecker so I left him alone. but every day I would find more insulation on my driveway. I think he was looking for a solid bottom in the wall cavity he had drilled into. I finaly said enough and filled the hole with expanding foam. Next day i found expanding foam all over my driveway and he was back at it. I refilled the hole with expanding foam mixed with nuts bolts hinges hasps, and other miscellanious chunks of iron. That finaly stopped him. He left and never returned. never tried to make a hole anyplace else.

We have had both woodpeckers (flickers) and cliff swallows try to make their nests on our house. The solution to both was hanging one or more CDs in the areas they go after. Just take a CD, such as the free software ones that internet service providers send out, tie a string or fishing line through the hole and hang on a nail or pushpin. We put one above each light on the porch, where the swallows were building, and several around the eaves in the places where the flickers like to pound. We found the flickers stay away from the side of the house where the dogs are.

We also found that after a while we could take the CD down and the birds would not return. And, even though we had maybe 10 of them hanging around, people just did not notice them up in the eaves or above the lights.