I have a CLK430 with 80000 miles on it. When I start in the morning I heard some knocking ( sounds like valves or head noise). But the noise will completely goes away after five minutes or when the engine is hot. I brought it to the MB dealership and they said that it's carbon buildup that cause the knocking. They said they need to remove the head to decarbonize it. I don't know if it's a good thing to do or is that the cause of the problem. Should I do any more reasearch before decarbonize it? Also, does 1999 CLK430 have a 8/80 warranty on the catalytic converter? Thanks.