It is nothing more than a slightly-educated guess. The noise is like a ballpeen hammer hitting a cannon ball; I assume that is nailing. The noise is way forward in the engine but short of the timing chain. The archives of this forum indicate that nailing will take place most often in the #1 cylinder. So I assume #1 cylinder. Maybe not the most exacting of empirical data upon which to base my speculation, but it's a start.

After reviewing the specs. graciously emailed by billybob, I may pass this job onto someone with more tools and experience.