With that info you just gave.
I would say your Flywheel is crack around the bolt circle.
I have had that happen before.
It is a (Clicking /Knocking sound)
.
I was at the Rod Run.
It was a Big Crowd
.
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The early bird gets the worm,
But the second mouse gets the cheese
84 Chevy K-20
63 Impala (my high school car)
http://67-72chevytrucks.com/vboard/s...Crew Cab Build