are the shoes worn? this may be just a need to "burnish" and "arc in" the shoes due to rust in the drum. A lot of major brands of fork truck in this size range uses the same brake shoes and wheel brake setup, and all have a "cold brake squeal" some of the time, in part due to the hardness of the shoe's lining materials.
MCFA had some instructions about dragging the brakes until they smoked to get the shoes properly "burnished" and I have seen on forkliftaction some suggestions about adding baby powder to the inside of the brake drum through the adjuster window (this was on a like sized Toyota, but they all use the same Akibono (not willing to look up proper spelling) brake setup