Your friend's flicker is either drumming, looking for food, or making a serious run at building a nest. Soft, weathered wood siding can also invite exploration by woodpeckers looking for nesting sites, though this is less common, especially on an occupied dwelling. If nesting or feeding is in progress, your friend's siding should have some visible damage. If there's no damage, the flicker is carrying out its annual drumming ritual. I suspect this is what's going on.
Woodpeckers drum in spring, for the dual purposes of attracting a mate and declaring a territory.
Each species has its own signature beat, the woodpecker equivalent of a songbird's call. For the next month or so, flickers and other woodpeckers across the US are drumming away. After this time, the racket should stop. Preferences do vary from one individual to the next. There are many nonlethal options.