I have an avalon arbor stove-4 years old. the convection fan has taken to loud screaming intermittantly. I have removes the set-up and given it a good cleaning but it persists. If I give it or the stove a god rap-it subsides for a while-which leads me to suspect a harmonic imbalance, but I just can't get it to go away permanently. I guess the only other diagnosis would be the motor bearings?? anyway, any advice or help is appreciated before I am driven to buy a new fan set-up.