I was having some noise issues as well. I stumble across a fix (in my case anyway). I noticed that when I lifted the keybed from the base, this noise went away. I cut out a square section from the foil layer in the base of the case where the keybed mouted. This eliminated the noise I was getting. In addition, I re-routed the keybed connector cables from above the effects board to under the keybed.
Worked for me, might be worth a shot!