otter4200

Ok so ive been trying to mod my Zoom G2.1nu to true bypass so that when im not using it i can step on an additional switch and have it completely out of my chain. I have done most of it and still cant seem to get it to work. This is a Diagram of the connection (using a 3PDT) . when the pedal is not turned on, the true bypass works and bypasses the pedal however when the pedal is on, i get this screeching noise.

And before you say it, i already know i could just make/get a true bypass box or i could buy a ready made true bypass multi fx.

So my question is, what can i do to fix this or is it not possible?

Cheers in advance!