Fmpnd: I have had hum problems too on all the higher frequency settings and all multiwave settings save PS2, but, as Drubin is asking, it was because the transformer in my equipment plugged into it (in this case, a dCS Purcell) started buzzing/humming, a common occurrence. In response to the original question, because of the buzzing and because my CD transport has an air pump, I have only used the PS2 setting, at Paul McGowan's suggestion. It certainly sounds better than any of the non-Multiwave settings to me.
