Tonight when I get home, I'll listen to the engine with a surgical stethoscope and let you know what I hear. The clacking noise happens predominatley when it's cold. I'll let you know what I find.

Going back to a comment Aquaticedge made about injector nailing, research indicates this is from the spring within the injector. Now since I've never rebuilt injectors, this may be a stupid question. Isn't that part of the nozzle?