Hi i have a 2011 Mercedes CGI blue efficiency convertible with a 155000 ks on the clock when i start it from cold i get a rattle for about 2 seconds then disappears definitely not cam chain noise it will run smooth the whole day with zero noises but when i leave it sit for about 30 minutes and start it a very slight rattle again ive been told its the oil draining back down in to sump and i need to fit a a camshaft adjuster oil control valve as they never come out with one does that sound right any help appreciated