For the past couple of years a woodpecker has been poking holes in the cedar siding of my house. The bird only seems to come in the fall. I've had an exterminator come out and there are no bugs. Could it be making a home for the Winter?
It's hard to say what your woodpecker is doing and why.
They do sometimes drill to communicate with other woodpeckers, or to try and get sap to run in order to feed.
And as you mention, it's possible it is looking for a good cavity, though we are not sure if this is the time of year they would do that. Perhaps new ones do go out to look for winter shelter.
Here is our page on woodpeckers: http://extension.umd.edu/hgic/woodpeckers-and-sapsuckers
You could call the Wildlife Information Center hotline which is run by the Department of Natural Resources and ask them if they have any further thoughts than what is covered on our link above.
Their number is 1-877-463-6497.