1995 Buick Riviera LOUD TAPPING OR KNOCKING FROM UPPER INTA

Noises problem
1995 Buick Riviera 6 cyl Front Wheel Drive Automatic 181k miles

I JUST PURCHASED A 1995 RIVIERA FOR 650, I WAS TOLD THAT I MIGHT NEED TO DO AN ENGINE, THE PERSON I BOUGHT THE VEHICLE FROM SAID HE DIDNT TAKE IT TO A MECHANIC TO DIAGNOSE PROBLEM. THE NOISE IS COMING FROM UPPER INTAKE MANIFOLD, (KNOCKING NOISE)MAYBE A LOUD TAPPING NOISE. THE CAR ACCELERATE OK, BUT THE LOUD KNOCKING OR TAPPING FROM UPPER INTAKE MANIFOLD IS MAKING IT HARD TO DETERMINE. YOU COULD PUT YOUR HAND ON THE MANIFOLD AND FEEL THE TAPPING. CAN YOU DIAGNOSE?