No ticking at idle (so it does not seem to be the oil tubes). It almost sounds as if it was pinging from low octane as on old cars, but I put 93 octane in it and I think newer cars compensate for that by changing the timing. Any idea what could cause this? Is there some type of sensor?

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2008 S550
2010 GLK350
1997 E420 (retired)
2005 CLK500 (retired)