The most famous and familiar woodpecker sounds aren't songs or calls, but drumming, which is also called rapping, tatting, and tattooing. Woodpeckers (in this case, a Pileated, the largest species in North America) peck on objects to create sound patterns as communication. Resonant objects such as hollow trees, logs, stumps and metal-wrapped power poles and chimneys are favoured for drumming because their resonance increases the strength and volume of the drumming so it can be heard further away.
In a particular area, birders can learn to decipher which woodpeckers are nearby just by hearing drumming patterns. But individual woodpeckers can tap and drum at different speeds and volumes, and sound travels differently depending upon weather and distance, so this takes practice!
Drumming means a lot more than just identification to the birds, however. A strong, vibrant drumming pattern indicates a healthy, dominant bird, one that controls a rich territory or would make a good mate. Both male and female woodpeckers drum, most often in late winter or early spring when they are more actively seeking mates and establishing territories.