giuliomoro I believe @lokki is similarly using the on-board preamplifier, right? Maybe shielding the cable inside the saucepan before it reaches the molex connector on the board would help?
right... but my vocal fx is never clean, so i would not hear the extra noise...
from the first post of the OP i get the impression, that the noise only appears when the rest of the gear is connected. (is that right @Taix ?). so i guess this could well be a grounding/wall power issue.
things to try to isolate the issue:
-pass-thru patch with only bela in the chain, is the signal clean on the bela output?
-pass-thru patch with loop station, is it still clean?
-original patch with only bela, clean?
power the loop station with a battery if you can, does the noise vanish?
power bela with a battery, does the noise persist? (i.e. powerbank)
does the loop station have different inputs, line/mic? maybe try a different input