I haven't so much as touched the engine compartment. Its totally stock. I plan to install a K&N oiled filter as soon as one is available. It's out for the ML320 (pass it along) and I'm told end of November for the E320.
The rattle isn't "bad" but its always done it after it sits awhile and is started. Since this engine is modular, have the V8 versions been doing this? No engine I've ever had has done this no matter how long it sits. If it's just the hydrolics pumping up, it may be no more than a start up noise "characteristic". But, if it is indeed a problem that will lead to engine problems later on I'd like to get the problem fixed. As well as the engine runs, I can't believe it a major issue...yet. Have about 8,000 miles on the car. It could be as simple as a stuck valve on the oil filter.
I'm going to have Mobile one synthetic oil installed with the standard 10W30 viscosity rating. And, I'll use a MB filter for this car. With the service intervals as long as they are, I can't see saving a few dollars on a critical part.
Thank you for your response.