Ahh I didn't do that. I just connected it straight to the pitch resistor. I have never made a vactrol but have heard about them - an led glued to a Light Dependant Resistor in simple terms. Of course there would be no current flowing though it to cause interference, I totally forgot about Vactrols.
Does anyone know a good light dependant resistor to use to make a vactrol. What is a good value to use, anything else I need to know. With the LED does it matter what colour I use, and how bright should it be? Is 5000 MCD okay/too little/too much?
Also.....I wonder if it would be possible to achieve the same effect using a transistor, putting the current from the 555 into the base of the transistor to control the pitch? I know nothing about transistors though, and wouldn't even know where to begin to start?