I made another chek with cables and power supplies, nothing has changed, but at least I understood part of the noise problem. Using the loop fx in serial brings noise due too feedbacks (and we know it), but in parallel, since the volumes are differents I have to blend the signal and, boosting the wet signal in parallel, there’s an evident flanging metallic sound coming, filled with high frequencies. This metallic sound, with the high gain of the amp, turns into my hated high pitch feedback.
Now I have to understand if is a peculiarity of the amp, or of the pedal. Waiting to test on another amp then, since my amps have an identical fx loop.
In the meantime, thanks for the help, I’ll update you.