I had a flex plate crack that sounded like a rod knock.
I had a knock only when driving my v8 s-10 that made me crazy, I was about to pull the engine when I discovered a wrench I had left between the top of the frame and floor, it would rattle against the floor sounding like an engine noise.
My v8 miata had a random knock that confounded me for a while turned out to be the purge valve was resting on the fender well and transmitting a knock every time it would purge, sounded like a random rod knock.