I've had some success with noisy foils by eliminating some of the hollow in the rear of the foil shape giving them more of a traditional shape. I don't know if the hollows were intentional or not. To see if you have them, hold a straight eged horizontally against the foil (in the direction water will flow). If you see a point where the foil pulls away from the straight edge leaving a "hollow", fill it and fair it.