slant 6 knock

slant 6 knock My engine has been knocking since last summer, I only drive it on the weekends in the summer, if the roads are dry. I got it out today and have been waiting untill I had time to check the valve lash. But when i opened the hood the knocking sound sounded like it was coming from the bottom end. :cwm10: I pulled the plug wires one at a time and when I pull number 3 the noise stops. My question is can this be an exhaust leak? #3 is behind the carb and I can't get at the exhaust manifold to feel if it is leaking. ( high hopes). When I run the engine at about 1500 RPM the noise stops also. My question is do you guys think it is a rod or can it be a lifter needing adjusted or an exhaust leak? I have a 340 to put in but I was going to run the 6 this summer and put the 8 in this fall. Please help? thanks walt :salut: