A guy I worked with years ago had a house on the edge of town and adjacent to some heavy timber. The woodpeckers were driving him nuts, hammering on the house and reducing him to ludicrous "scare" tactics that all failed.
Somebody at a local watering hole suggested that the "natural" wood siding on his house was full of tasty - to a woodpecker, anyway - bugs and larvae, so he re-sided the house. Whether the advice was legit or not, the woodpeckers never came back.
Sometimes insects like Mason bees or Carpenter Bees, or other solitary bees will go up under the exterior course of shingles use the spaces between the interior layer to deposit their eggs/larva. This could be what they were looking for.