1998 Chevy Astro 98 ASTRO VAN KNOCKING

I HAVE A 98 CHEVY ASTRO VAN.IT FIRST STARTED WHEN MY VAN STARTED TO LEAK COOLANT FROM THE THE INTAKE MANIFOLD.SO I TOOK THE MANIFOLD APART AND REPLACED THE GASKET.A LITTLE COOLANT GOT INTO THE OIL.SO WHEN I WAS DONE REINSTALLING THE MANIFOLD I ALSO CHANGED THE OIL AND FILTER.VAN RAN GOOD FOR A WEEK THEN I STARTED TO HEAR A SMALL KNOCK.THE MORE I DROVE IT THE LOUDER IT GOT.(ONLY AT IDLE)WHEN I'M DRIVINGTHE KNOCKING GOES AWAY.ALSO IN THE MORNING 1ST START UP OF THE DAY DOESN'T KNOCK FOR 3 MINUTES.THE WARMER IT GETS THE MORE IT KNOCKS.(IDLE ONLY)I'VE REPLACED THE FOLLOWING OIL,OIL FILTER,SPARK PLUGS,WIRES,ROTOR,CAP,INTAKE MANIFOLD GASKET SET,WATER PUMP,EGR VALVE,KNOCK SENSOR,HYDRALIC LIFTERS,UPPER & LOWER RADIATOR HOSES,RADIATOR RECONDITION.OIL AND WATER DOESN'T MIX.WHAT WOULD HAPPEN IF DEX-COOL GOT INTO THE OIL CRANK CASE?(I SEEN ARTICLE 99 ASTRO AWD LOWER END KNOCK)1 MECHANIC SAID I MIGHT HAVE CARBON BUILD UP AND HAVE PRE DETINATION.WHAT ELSE CAN IT BE?THANKS FOR YOUR TIME!