help? - pedal sends out high note or no sound

Hello, I have a problem with my pedal shield.

when I use it with the pedal on it sends out a high screeching note like a sonic cat repeller
and when I use it with the pedal off the pass-through doesn't work so I get no sound.
when I move around the power cable the volume of the high note changes.

any tips on what to look for when trying to fix it?

thanks, Lazz