Same howling noise here

Ok nx , I will try to help you .
1 ) unplug the refrig , and on the back , remove the panel covering the
board.
2 ) unplug the blue conector on the board , with 3 larger wires connected to it . looking at the connector , you will see
wire1 , wire2 , space , wire3 .
3 ) find a short piece of insulated wire , and strip both ends about 1/2 inch , and insert one end into wire2 , and the other into wire3 . Leave the connector unplugged .
4 ) plug in the refrig . After about 1 min , look inside the freezer , at the bottom , looking for a red glow . If no red glow , then the problem is the heater or defrost thermostat ( the 1" cylinder , with a pink and blue wire going to it , clipped to the top right on the coils ) . If you replace the heater , replace the defrost thermostat also .
5 ) if you do get a red glow , then the # 4 thermistor is probably bad . This is the 1" white torpedo looking piece , with 2 wires going to it , clipped on the top left of the coils . This thermistor works off resistance by coldness , and sends the signal to the control board . When the control board registers this resistance for so long , it will go into the defrost cycle , causing the heater to come on .

The fan howling , could be from trying to pull air up thru the frosted coils. The # 5 thermistor , located at the bottom of the freezer , slightly foreward of the drain , inserted into a holder , with 2 white wires going to it , tells the control board what the freezer temp is . This thermistor , could be bad , varying the resistance message to the control board , causing the fan speed fluctuations .