9 years later yes, same here in my 04 w211 wagon with 85K miles and over a year I now have 120K. I loved the smooth sound of the straight six E320 and was not as happy with the V6 which does have vibration and knock. I nearly test drove a used car in order to compare but just feel its the vibration pattern of the V6. Under heavy throttle its gone and also at smooth idle, just hear it at lower RMP under light load..low knock with a bit of a ring to it as well. Glad to hear others are concerned and its not just me.