Engine "Tick"

My nephew, Elijah, was visiting us (during my father-in-law's funeral) last week, when I learned he is a "car guy". So, I took Eli out to the garage to show him the Dart.

I started the Dart as usual, but it now has a very pronounced "Tick". This tick increases with rpm. It has a cast iron ring to it, like your tapping the block with a small hammer. Oil pressure at (fast) idle is at ~50 psi (normal). This tick has appeared many times in the last 12 years or so (as long as I've owned the car), but has always disappeared after a few minutes of warm up.

This is the original 318, 2-bbl with ~115,000 miles on it. I do not believe it has ever been apart.

Where do I begin?:confused: