This is a GE refrigerator defrost heater turning on. I’ll go over the defrost operation for you. The evaporator develops a thin coating of frost during normal operation. This is caused by condensation, which deposits itself, and then freezes, on the evaporator. If this is not burned off it will get thicker and thicker until it inhibits airflow across the evaporator coils. If this happens the fresh-food section will get warm.