I've been having this problem with my POD500, I'm not sure if its always been this way as I've only recently started using clean sounds as opposed to distortions or boosts. I play through either a VOX Amp or through a USB connection to my laptop in the garageband interface.
I have isolated the issue to the POD500 and a very distinct buzzing noise can be heard even without any effects blocks or boosts of any kind with my AMP having no gain. I've researched that this might have something to do with the power outlets not coming from the same socket but even when I detach the charger from my Mac the noise still remains...
However, when I remove the POD500 from the equation and have it running straight from guitar to Amp, it's silent.
Can anyone help?