Date registered: May 2016
Vehicle: 2000 S430, 2003 S430, 2003 S600 TT, and 2005 E320 CDI
Mentioned: 170 Post(s)
Quoted: 965 Post(s)
My '03 S430 used to do that, too, though not quite as loud. In my case, the solution was two-fold.
1.) I did engine oil/filter changes every 5,000 miles, and with each oil change, I'd put in a quart of Marvel Mystery Oil. The first three oil changes went like this (I got the car at 139,000 miles and change). The last one that I did, about 1,200 miles ago, was straight engine oil. Not sure if the MMO actually did help any; maybe it did, maybe it didn't.
2.) On a business trip two years ago, I asked if there was the option to drive, realizing that the S430 hadn't yet had a road trip. Boss said yes, just keep your receipts. So, I did an oil change the morning before departure and then used that car for the trip. It was a 1,600-mile round trip, and the car seemed to really like it.
That engine started getting quieter after the second oil change. It continued to gradually quiet down as time and oil changes went on. Now, there's still a very slight tick, but nowhere even close to what it had been earlier. It is also considerably cleaner under the valve covers than it had been. Part of that last bit is some work with kerosene and a toothbrush when I did the valve cover gaskets. Part of that is regular oil changes.
It appears that following the dashboard "A service" recommendations may not be the best idea, long-term, for the engine.
2000 S430 (Dad's car, used for special occasions)
2000 S500 (wife's DD: my first W220 project car)
2003 S600 ("sex on wheels"--second w220 project car)
2003 S430 (one of two current DD's--third W220 project car)
2005 E320 CDI (the other current DD--first W211 project car)