I have a 1999 E320 4M Wagon (110K) and a 2001 E320 Sedan (52K) that occasionally "chug" or "tick" after reaching operating temperature. After driving at 45MPH and stopping at a traffic light, the engines will run extremely smooth but emit a subtle clugging noise. Has anyone ever experienced this problem on the M112s/M113s? Could this be a result of worn valves/lifters that have been discussed on this forum previously?

Also, a rattle can be heard under the wagon when in gear (reverse or drive) after cold starts. Does this indicate that the cats might be going bad? (I had to replace the converter on the 2001 under warranty.)

Mobil1 5W40 (initially 0W40) has been changed every 5K on both vehicles. (I know this is overkill, but the cars are used for city driving.)

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