slant 6 knock

Clicking/ Tapping/ Rapping/ Slapping is usually top end noise but the bottom end can start this way, heavy knocking is botton end. Is the sound at engine speed or twice engine speed?? engine speed noises are engine problems from the piston down. Twice engine speed noises are the Camshaft and up. You can put A long screwdriver on different engine parts lower block, valve cover, exhaust manifold etc. and listen at the handle similar to a stethescope, the noise will be more obvious near the problem area. I have found bad Alt bearings and bad valves this way.