My 85 190E developed a loud tapping/knocking noise that seems to come from somewhere under the valve cover in the area of the last cylinder(#1) and is loudest on the intake valve side. I changed the lifters and the rocker arms as well as the camshaft but the noise only got worse after the following oil change. The noise appears once the engine has warmed up. No noise when it is cold and warming up. I talked to the mechanic who rebuilt the cylinder head before I got the car and he suggested it might be piston slab?!. I would very much appreciate any suggestions on how to proceed to get rid of the noise. Thank you very much in advance.