My 2003 S430 is experiencing some clicking noise, coming from the top/passenger side of the engine. It only does it in idle and, only after it's warmed up. The noise goes away when I accelerate. A mechanic told me it was the lifters, which were replaced but, it's still there. Another MB owner told me it could be the tensioner pulley. I don't want to continue to replace parts, just for replacing parts. Has anyone experienced this same issue? I would appreciate some guidance.