Go underneath and check the pulley to harmonic balancer bolts. You may have one or a couple bolts too long making them scrape against the timing case cover.
Had this happen on a 68 Roadrunner with 383. We did a new rebuild. On start up we get this noise we could not find.
With the engine off, went underneath , noticed that the pulley to harmonic balancer bolts were too long and scraping the cover. We put shorter bolts on and no more noise.
After a new rebuild and learning it was just a bolt... wow that stinks. I'll check the bolts tonight.
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"Id rather have a bottle in front of me than a frontal lobotomy" Ben Franklin 1755
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