So, here's the story:
We hear a knocking sound at the south side of the house; a rather strange, sharp hammering sound, but somewhat arrhythmic.


A quick look out the kitchen door confirms the suspect - a woodpecker. And the little beggar is modifying the entrance hole to a birdhouse.

Some research in the Audubon book yields the identity of the aforementioned beggar and the probable intent:
- female Downy woodpecker (no red patch seen on the back of the neck, size smaller than a robin),
- woodpeckers will thump on a dead tree limb, or similar material, to announce their presence and declare their territory. In other words, the little beggar was drumming, or
- the house hole may be marked for future use.
It might be nice to have resident woodpeckers, but they do make some weird noises.