Rebuilt 340 knocking sound

You would be amazed what a hot tanked and never started rebuild will look like inside after sitting for 1 1/2 years.
I live in the Humid South. And when I build something, it's in stages. Yes, I'll bag em up, but they are stored outside. I've never seen no crazy crap like that. HOWEVER, that's an Engine every now and then. Not a mill a month.... so my experience Don't make me the Be all, End All Authority