It is likely that your refrigerator section defrost drain is blocked, causing defrost water to build up behind the backpanel in the refrig section so high that the ice hits the evaporator fan.
To repair, you'll need to remove the back panel and unblock the defrost drain. Unplug appliance and open refrig doors for at least 45 minutes before attempting to remove refrig section backpanel. It will be "iced" in place and is difficult to remove. Use a handheld steamer to thaw ice as you attempt to pull out the backpanel. Be careful -- it's easy to damage the styrofoam behind the backpanel. After you get panel loose, unplug fan and sensor wires and remove. Now continue thawing all the ice build-up and make sure water flows down the drain at the bottom of the evaporator (cooling tubes). The backpanel will likely also have ice build-up around the evap fan. Remove 4 screws to access the fan and melt the ice.
To prevent defrost drain from clogging again, take a 2" long piece of #12 or #14 copper wire and bend a 1/4" diameter loop in one end. Stick the copper wire down the defrost drain and attach loop to defrost heater. Use needle nose pliers to tighten loop onto the defrost heater.