Have someone check that the drain is handling ALL the water from the cooling coil, the pan might be off level, so SOME of the water is dripping down. (Also check that there is a secondary pan to catch water if the drain plugs up.)
Then check the ducts to see if water is condensing on the INNER surface of the duct under the insulation. Water condenses out of the air onto the coldest spots, so seek. If so, you need to seal the OUTSIDE of the duct runs.