I have a combo bass/guitar board with ~10 pedals. I have isolated one of the most significant sources of noise to the interaction of two pedals. The first is a Morpheus Droptune. It is digital, allegedly true bypass, and needs a 12V center-positive power supply. The second is a Hardwire TL-2 (their take on the Metal Zone). It is analog, allegedly true bypass, and takes a standard Boss-style PS (9V center-negative). Here's the issue: when the Morpheus is in bypass and the TL-2 is on (at pretty high gain; it knows no other setting), I hear a high-pitched hum. Not gain hiss, but hum. The TL-2 is my most high-gain pedal, I haven't fully tested whether I can replicate this with my other dirt pedals (B7K, Empress Multidrive). When I engage the Morpheus, the noise largely goes away. Now let me be clear: I don't really understand the practical electronics involved. I barely know what a "ground loop" is. The question I have is, given these circumstances, will a filtered, isolated power supply help, or is something going on with the Morpheus and/or my board arrangement that will create hum no matter what I do?