Is it possible that you have an exhaust leak on #1 cylinder. They clack and go away when heated up.

Have you listened via a dowel rod to the engine. Dowel against the Valve cover and other end at your ear.Place the dowel on the VC at each cylinder. Put it on the alternator, air pump, etc you'll likely find where it is really coming from. An Auto stethoscope will work too.

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1986 Euro 500SEC "RUF" 9:1CR, "Rose"
1985 Euro 500SEC Cabriolet AMG Widebody
1982 Euro 500SEL "Blue"
2001 Texas Heeler (Aussie/Queensland X) "Sulphie",
2012 Queensland Red Heeler "Squeak"
Best dogs I've ever had.