A week ago my K5's engine started to make some sort of knocking sound.It's not constant.First I didn't know where it was coming from.After little searching,I located it to a cylinder #2.I went under the truck,and by using long screwdriver,I tried to listen from the oil pan that was the sound coming there.Nothing. Then I listened from the valve cover.And it was definetly #2.I loosened injector line and the sound was gone.Tightened the line,and the knocking sound was really loud. Engine runs smoothly on idle.So I guess it can't be bad injector. Previous owner had changed one piston,because it had broken,abowe the pin.It was just went pieces from there.But if this is the source of that sound,I could hear it from oil pan,too? What could be the problem?Lifter?