Hi. I've just build a RAT using the main layout. Sounds awesome but I've noticed that there's a continuous hight pitch noise when no input guitar cord is connected. Of course when the circuit it's ON, in bypass there's no noise whatsoever.
Yeah, it does that. I built a stereo Rat for a synth guy and I ended up using switched jacks so that any unused channels were grounded. That way it could be used in mono without the squeal from the other channel.