W203 (C230K) Engine rattle (timing chain?)
 

A few days ago I'm driving one quiet day with the music off, and hear this very quiet rattling noise coming from the engine. The noise appears on very brief moment just when I push the accelerator pedal, quickly disappears, and comes back for a moment when I release the pedal. Over the weekend I tried to pinpoint the location of the noise - looks like it is coming from the timing chain area. Interesting thing that when the car is not moving, I need to rev the engine higher to get the noise - about 2200 rpm.
I had issue with the cold start timing chain rattle year ago. I have replaced the chain tensioner and the valve adjuster. Could the new tensioner gone bad? Or this noise can be caused by something else?
The cold start noise was similar, but much louder than this one.

I dont know, but mine did this with no failures for over 100k........common on this engine

I'd get a mechanic's stethoscope and try to pinpoint where exactly it is coming from. Sounds bounce around in an engine compartment and sometimes noises seem to come from completely different areas than where they actually originate.

Also try the area around the belt tensioner/tensioner shock.

I have looked again today and tried to determine where the sound is coming from. Without the stethoscope - did not find one yet. Looks like it originates where the cam sprockets are. I think I'm going to take off the cylinder head cover tomorrow and see if anything there looks out of ordinary.

The rattle you are describing is probably the Magnetic Cam Adjuster. You might want to pull the connector off to check for leaking oil... it's not good for oil to seep up into the harness.

I have replaced the adjuster one year ago, along with the magnet and the chain tensioner. Seen and fixed the oil leak you mentioned, too.
The problem that I did not install it right first time when I done the replacement. The adjuster consists of several parts that slide one into each other...long story short, I did not slide them in all the way. I got lucky (or so I thought) - the only problem I've experienced was the check engine light because the magnet could not pull the adjuster core anymore. I reassembled and reinstalled everything, the light was gone, and I assumed that the incident is resolved. But maybe the adjuster experienced some premature wear because of this.. have no clue. Maybe it is not the adjuster at all.
Anyway, anything you'd suggest me to pay attention when I take the cover off? In particular I'm interested if I can (or need) to check the tension of the timing chain.

Took the cover off today - found nothing (as I suspected). Timing chain fine, not stretched, guide rails fine as far as I can see, hard to say about tensioning but it looked ok to me. No signs of any damage anywhere.
After that I did some googling, and found this topic. As Will_w202 wrote, it is a common problem, apparently. I pulled the adjuster magnet plug to test - rattle is gone :) Now I'm thinking, should I shell out another $500 for yet another adjuster and spend half of my weekend on replacement? I guess I'll drive with the rattle for now ;) unless it will annoy me a hell lot more.
Thanks for suggestions folks!

Hmm, now that you mention it, it turns out my engine does this too! Car seems to run fine with the rattle, anyone know what the downside is of leaving it? Worse performance? Timing chain wear?