If you have a knocking noise from your engine it might not be the engine itself. I have seen on occasion the torque converter bolts get loose and cause a knocking noise that sounded very much like loose engine parts. So if you have a knocking noise and an automatic transmission, it’s a good idea to check the torque converter bolts to see if they’re tight. If not, snug them up and recheck for the noise. Come to think of it, it’s a good idea to also check the flex plate for cracks. Sometimes the flex plate will crack and as a result it can cause noise. So while you’re in there, check the flex plate for cracks or damage, you might just find the source of your noise this way.