Sounds like the defrost drip tube is clogged, so when the freezer goes into defrost mode, the ice melts and the run-off water has no where to go. Look for a tube that runs out the back or underneath into a catch pan, and blow into it hard (like blowing up a balloon) if you heard bubbling like a straw in a drink... be aware you may just get a mouthful of water. if air won't go through, you may have to unclog it from the inside of the freezer by disassembling the interior back panel. If you are not comfortable with this call a service tech; and as always, unplug your frige before servicing