Woodpeckers communicate in two main ways. The first is through their vocalizations, which are often loud and strident. The other method of woodpecker communication is called drumming. Drumming occurs when woodpeckers rapidly strike an object with their bill many times in quick succession. In the past, most drumming was done on hollow trees. The woodpeckers of today still use hollow trees, but also use things like telephone poles, metal objects on houses (such as dryer vents), and many other modern conveniences. The purpose of drumming is similar to that of woodpecker song-proclaiming territory ownership.
So the next time a Gila Woodpecker is drumming on your house at 5AM, you'll know why. Won't make it any more tolerable, but at least you'll know the reason why.
Doesn't seem to do any damage, but I can't stand the noise, so I chase it away every time I get a chance. Damn 'gutteral' Woodpecker.