Hi Dan.
My foils are taken from moulds that I had built from plugs I made employing sections developed using NACA design principles which call for 'squared off' trailing edges. They are vac. bagged carbon/foam laminates, very straight and very strong. To sharpen the trailing edge would seem counter productive given that one rudder and one d/board are noiseless so it's probably not the squared trailing edge causing the problem. They are also finish blocked with 1200 wet&dry and their surfaces are fair and straight.

Bern