Rotosphere: unplugging then plugging back in stops buzz?

[ruger9]

Sometimes I'll turn my rig on and it'll have a pretty bad buzz. If I unplug the power on my Rotosphere, then plug it back in, the buzz is gone. Anybody know what this is, and how to fix it? I mean, doing what I'm doing fixes it, but I sure would like a permanent solution.

RS is plugged into courtesy outlet of PP2+, which every pedal I own is also plugged into, no diasy chains. Pedalboard is silent.