My truck has a tick too that I haven't figured out. An old mechanic told me a trick to diagnosing that is to hold a long screw driver against the valve cover and put the other end to your ear, and then the same from the manifold. Wherever the ticking is loudest through the screwdriver, that's your dealio. I haven't tried it yet, but the idea seems to make sense. You can find car engine stethoscopes too at any car parts place, same principle.