Love your stuff, Scotty, and hope you can help ID my problem. Got a 2004 Navigator that's developed a knock just like this - https://www.youtube.com/watch?v=Zl4NqsAi6WY. It's got 200k miles and has a long history of misfires from faulty ignition coils. Is this a rod knock or stopped up catalytic converter?

that's really loud internal engine noise, from what I hear. I would get rid of it pronto rather than spend thousands rebuilding the engine

Damn, sounds like a diesel with that knock