2002 Mercedes Benz C230 Engine Noise at Startup

I get a noise at cold startup for about six seconds. A clattering I would describe as similar to putting a baseball card on the wheel spokes of a bicycle attached to the frame of the bike with a clothes pin like I just to do when I was a youth.
I purchased the vehicle new in October 2001 and since it is garage kept and well maintained. It is in excellent condition I have another car for daily use, I intend to keep it for many more years.

I had brought the vehicle to the Mercedes dealer twice, the first time a year ago and the second time a week ago. The first time two years ago they did not hear the noise, the second time they heard it but were unable to diagnose it after having the car for a week. Fortunately they did not charge me and informed me that it would be $1,000 to start a more intrusive investigation including removing valve cover and spark plugs and putting a bore scope down into the combustion chamber. Mechanic diagnosed it as possibly the cam adjuster on the intake cam or possibly the surge valve.

I have investigated doing the work myself if it is the cam adjuster for which I found available online for $683.38. Adding up all parts cost including the adjuster, exhaust cam gear, timing chain, timing chain guides, chain tensioner etc. Add up to about $1500 in parts alone.

Since first hearing this noise I have driven the vehicle on several 900 mile trips consisting of 14-15 hrs. Of straight through driving with stops only for gas, nourishment and rest stops with no issue or change in performance.

I would appreciate any input you can give me on this.