Voodoo Lab

Hi Everyone,
I'm new to this forum and apologize if this topic has been addressed.
I have a Strymon El Capistan powered by the PP2+ using input jack 5 / Normal running into the FX loop of my Friedman BE100.
With the loop engaged, I noticed a significant buzzing coming from my amp. If power the Strymon pedal using the supplied 9v power supply instead of the PP2 my amp is dead quiet. Any thoughts or work arounds to this problem ?

Thanks,

Steve