87 300sdl 3.0 noise

[tenmaz]

I hear a metal tapping noise dead center on top of engine. I opened oil fill cap but could not hear it any louder. The tap makes 7-8 taps seemingly in time with the engine, then stops briefly 1 maybe 2 seconds then taps 7-8. This pattern continues consistently. The cooling temperature is fine, and oil pressure is fine. However, I had just changed the oil and filter 3 days ago. Before this there had been no sound. 286k on motor it had been running great. I've been running 100miles at 70 getting 30/gal. Any tests or repair suggestions will be appreciated. You all have been a great help in the past thanks!!