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!