Has it been run with the valve covers off? Or a cover with an opening to hear if it is prevalent to one side?
Is the noise louder at low rpm or just drowned out by other noise? I’d look to eliminate any noise you can....exhaust especially! It may be louder (or not) at increased RPM....and therefore more discernible.
I really think if parts were interfering they would ‘self clearance’ by now, or be producing a lot of shrapnel.
🤔
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