[Motor31]

Before you decide to replace the fan take a look at it. If all the blades are there it's just vibrating too much on the mount. That sound was what ours was making from day one. I pulled the cover down and saw that the motor had 2 legs on it that mounted parallel to the mount holding the assembly in position. I took some wire (in my case aircraft safety wire) and put tension on the legs. Each set of legs in close proximity got tied together dampening the vibration. The fan is nice and quiet now and has been for over 3 years.