This shows the cold startup on a 1992 400E that had not been started in 1-2 weeks. Note the sharp rattle noise from 0:05-0:07 in the video which goes away entirely by 0:07. The rattle will not occur again until the car sits overnight or longer. This issue primarily affects M119 engines produced prior December 1992 (which is mid-1993 USA model year).
One main cause is the drainback valve in the oil filter housing. Sometimes, upgrading to the newer style valve will help or cure the problem. Details are in the following TSB's:
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The other possibility is the cam adjuster springs, there were 3 versions, and sometimes upgrading to the latest style (thicker wire diameter) spring may help - see bottom of page 3, FSM job 05-2170... but it's a LOT of work to replace these springs:
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There have been some cases where both the drainback valve and adjuster springs were upgraded and the noise was not completely eliminated. An MB dealer master tech mentioned that he talked with an MB engine development engineer, who stated that adjuster rattle will never hurt anything.
If your engine sounds like this at cold start, you probably don't need to lose sleep over it, especially if the engine is a 1992 or older. If it's 1994 or newer, or if the noise occurs at a warm startup, further investigation would be prudent.
