I have a 1990 190E 2.6L and when I start the engine I hear a weird noise.....hard to explain sort of like a low "clum-clum-clum" noise coming from the engine. I have a leaky valve cover gasket for sure that I need to replace, so while I have that of I would like to know if anyone has any idea of what it could be under there making that noise and what I need to do to resolve it. Thank you for your help in advance.