If it was out of oil I would put my money on a spun Rod bearing.
Been there and done that. Not that it could not be up in the valve train but I would bet otherwise. Drop the pan and wiggle the rod ends, that is easier than going thru all the rigamaroll of trying to track down a noise that may or may not be in the upper end.If nothing is wrong then bolt the pan back on,count yourself lucky and then start the process of elimination up top.

Have a good one,
Dan