Due to the heat from the burner below the fan on the J&S unit, the bearings dry out and therefore there is a squeal sometimes. Also, dust deposits can accumulate in the fan unit causing imbalance.
Try removing the fan by unscrewing the casing hold down bolt and removing the 3 wires or AMP plug. Clean down the unit and the motor can be taken apart and the bearing lubricated. Have just received a new fan unit and overhauled the previous one successfully.
jon seed, February 2008
