1987 Pontiac Trans Am

The tapping may be a noisy valve lifter, you will have to get a cooling system pressure test done to help locate any external coolant leaks, start here.

Mark (mhpautos)

I agree about the pressure test, but the tapping if it's not in time (rythm)of the engine and more like a tinny rattle, could be either a heat shield on the conveter or pipes(exhaust), or a heat riser with a broken bi-metalic sprig, it's right at the bottom of the exhaust manifold and the top of the Y pipe.