When you say "Sounds like a diesel", do you mean that it sounds like excessive clearance in the connecting rods? Loose piston pins? If the noise is right near the oil filter, I would check my connecting rods, starting with the rear-most rod. You could have one that overly large inserts for a larger size crank pin ie, your crank pins were reground .010 undersize, but one rod has a .030 undersize bearing. That excessive clearance will be audible if it is large enough. Also will cause a large amount of oil to drain out, potentially depriving the rest of your engine of adequate lubrication.
J. B.
