Probably a clogged drain line. Pull out the fridge to get access to the back. Remove the top bracket that holds the drain line using a small socket - either from a rachet set or a 6-in-1 screw driver will work (remove the driver head). Pull out the top section of the line and blow hard into the tube - usually a clump of dust that will blow out into the drain pan. Long term you should clean out the drain pan of any excess dust - looking to do this myself.