M156 head damage, can't find source
 

2011 ML63. 168k miles. About a week ago started getting a loud rattling noise for a couple seconds on cold startups. Noise then disappears completely and runs totally fine. Suspected a broken camshaft adjuster. Just took the valve covers off and so far all 4 adjusters feel tight but I noticed gouging and what appears to be a crack in the head near the adjusters on the passenger side. Any ideas what could have caused this?? I don't see any metal shavings in the little pools of oil sitting in the head but I'm looking forward to doing an oil change and checking the filter. Nothing looks obviously broken.

I do need to go back and double check the adjusters, my adjustable wrench isn't quite fitting on properly.
https://cimg1.ibsrv.net/gimg/www.mbw...a944fa2bcf.jpg
https://cimg3.ibsrv.net/gimg/www.mbw...57df8d9f9f.jpg

The 'crack' in the top seems to be nothing, it matches the driver side, looks like the heads were just made that way. But the gouges are real and appear fresh. All 4 adjusters seem tight too. I'm at a loss...for now.

Here's a video of the startup noise in case it helps

any update? Sure sounds like adjusters. Instantly stops when oil pressure builds

Yes, it was the passenger side exhaust adjuster (right next to the gouges in the head). It originally felt good with an adjustable wrench but I ended up ordering a set of thin open ended wrenches and immediately found that one was loose/broken, the other 3 were okay.

I still don’t know what caused the gouges in the head, I changed the oil and inspected the filter and all looked fine.

I need to go back and reseat the passenger side valve cover, one of the bolts didn’t want to thread in properly and now it’s leaking. Otherwise the noise is fixed!