Stock HD brakes do not have spring retraction. When you apply the brakes, then release them, eccentricities in the disc are what push the shoes back. Stock shoes do tend to sing a bit, as they float on the surface of the disc. My Lyndall Z-Plus pads sing less, and produce almost no dust.
It could be that you have a slight baked-on dust accumulation ridge on your pistons that hinders retraction. Such can be cleaned off.
Enjoy,
rich P