Have you upgraded the power input cord or done any of the other recommended improvements to the supplied power circuit, per the manual? According to the manual, PS Audio recommends that you enhance the power cord for optimal results and also replace your receptacle with one of their other products which clean up the voltage coming from the wall.

Contact your power company (PECO) and ask them if they can tune the transformer for your neighborhood to provide a higher stability voltage. Unless I am mistaken, PECO has several Nuclear Generating stations in their grid so the power should be pretty clean.