Guitar processor noise...? BZZZZZZ!

**** Pishta LOLOL You oughta know how to wire a "tip sleeve" connector. Yeh the sleeve is one conductor and the shield. This is actually poor design. Much better if it ran a "shield only" plus two BALANCED wires (telco style) for the signals

I assume you've tried moving / wiggling/ shaking components/ cables to see loose connnections or maybe if SOMETHING EXTERNAL is inducing noise.

Might be the power supply is overloaded or defective? Get a meter on a DC point and look for ripple with the meter in AC mode. Ground the input of the offending component and see if it still buzzes

Take your meter and look for continuity to ground on the output jack. Maybe it's capacitive coupled and is putting unwanted "leakage" through into the amp

Also take your meter and with the component and then the amp powered check for EITHER DC present from the outlet 3rd wire to the audio jack grounds. Should be NONE

AND make darn sure the outlets are actually grounded properly--and that there is NO AC from 'actual ground' like a water pipe to the 3rd wire of the outlet/ strip/ etc

My ex super at the wheelchair joint plays guitar and played way back when he was young. He and I have discussed some "gigs" he got into where a guy got shocked or damn near electrocuted by cords, mics, etc, that were "hot" because of poor grounding. Back then lots of places he played had poorly wired or non grounding outlets