I wonder if you dropped your oil pump pickup screen and it's banging around.
I smashed my oil pan on my '65 CJ6 many years ago chasing my brother on a trail one day. I came down real hard on a rock and the reinforced pan actaully bent enough to contact the bearing cap on one of the connector rods. I drained the oil and simply banged out the dent and away I went.
Good luck and let us know what you find when you drop the pan.