Excuse me if overlooked any similar threads while searching for an answer here. I recently built an IC Muff using the tagboard FX vero layout (seen below). While it sounds just as good if not better than my original IC muff, it has a strange quirk in that it starts to create a sustained whistle when no notes are being played, when the tone and sustain controls are dimed with the tone stack engaged in the circuit. When I back up off the tone and sustain controls a bit to 3 o'clock each, the whistling goes away and it sounds fine. When I bypass the tone stack, it goes away completely and acts just like it does on all settings like the original. I double checked everything and it all seems to be in its right place (it initially didn't work because of a bridge I forgot so its been well troubleshot). If it matters, the IC's I used are for IC1: RC4558P and for IC2: LM471CN. Has anyone encountered a similar problem before and know what went wrong and what to do about it? Or where I should start investigating on the circuit board? Any help would be much appreciated!