This is a bottom freezer unit. The fans are still circulating air in both compartments and the unit is cooling properly. I'm wondering if plaster dust from a remodeling project may have caused the problem . . . I didn't clean behind and under the unit until after the noise started (I also cleaned the fan located on the back of the unit). The noise occurs when the motor turns on . . . if it is a bad fan motor, how do I determine whether it is the condenser fan or the evaporator fan???

The noise lasts as long as the motor runs but sometimes quiets down before it shuts off. I've listened carefully, but can't determine where the noise is coming from. Maybe I should pull it away from the wall and try to listen closer to the back of the cabinet??