I baby this car on ignition, giving it a good 1-2 min. cold weather before putting in gear, and I don't push any engine during its first 500 miles. But the "ticking" has now become a much more audible tapping/chatter that's even more pronounced on acceleration, when you can hear it even over the well-tuned exhaust pipes and road noise and it is just short of a knock.

Plus, after I start the engine cold, as the engine warms, and drops to about 850 RPM there starts to be a slight but perceptible shaking to the car, gets more pronounced as revs drop to the lowest point for idle, about 600 RPM.

Engine, warm and idling, with hood open, sounds like there is a typewriter in it; most of engine is smooth but 1, maybe 2 cylinders have a loud, thin metallic tap on every cycle.

I haven't done anything driving-wise to damage this engine. I don't buy that it's "injector noise." Ticking becomes tapping becomes clacking/chattering, sounds just like the perennial lifter noise I had for the last 10 yr on my Voyager.

I don't think I'm a "noise freak" but I expect a Mercedes engine on a $30K+ car with <500 mi. on it to purr, not chatter like a tin toy or clack like a tired old 140HP, 4-cyl. minivan. Taking beloved Xfire in today.