Kemore model 795.7731 bottom freezer

Question

The fridge has started making a loud buzzing or whining noise when it is running. Just started in the past week. When you open either top door or the freezer on the bottom, all noise stops. It's like the motor shuts off. As soon as you close the door, it starts up again. I did notice frost buildup on the back of the freezer compartment. Do you think it is the evap motor making the noise? The fridge seems to be cooling and freezing ok for now. Thanks!