Mystery solved, sort of.
The keys clicking under my fingers just now have been traced back to a radical coalition of people in California. Calling themselves the Bay Area Response Team (BART??), they are a loosely organized cell with a history of generosity and extreme kindness.
Several days ago, I received a note claiming responsibility from the supposed leader of this group. Early indications suggest that he is a remarkably intelligent, highly skilled, unborn child of promise who is highly revered by his followers.
We consider the matter resolved, though our investigation will continue to remain open.