Listen to the noise, and you might be able to narrow it down a bit.
If the noise is constant at 1/2 engine speed, think rod bearings, they only
knock on the firing stroke
If the noise is constant at engine speed think piston problem, bent rod, or
the dented oil pan that mentioned.
If the noise comes and goes at 1/2 engine speed look for a dropped valve
seat.
If the noise is random (not at engine speed or 1/2 engine speed look for a
pulley or whatever.
If the noise is at 1/2 engine speed try pulling spark plug wires one by one,
if the noise gets quieter it is a rod bearing for that cylinder.
Good luck and I hope that whatever it is, isn't too expensive.
Rick
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