Going by what your saying about the knocking, I'd suggest doing one of two things, if not both. That's NOT running the motor, until it's done.
Drain the oil, and pull the oil filter. Use a magnet, and look for any metal in the oil. Cut the filter open, and check it. That's the first thing.
Second, would be to pull the valve covers, and look. There's plenty of hiding places in the block valley, that oil (and metal) sits. Look for any signs of 'loose' metal, mostly it will show as powdered metal. Means a part is going away, slowly being ground down.
Also look the cam lobes over real good.
Your engine...your choice!