Arduino noise in audio circuit

I build my own guitar effects boxes. I tried to make a tremolo with one but the arduino puts out a high pitch noise. I does this regardless of any circuit. Just plugging one into a breadboard and powering it up
gives this noise even if there's nothing else connected to the arduino. I tried adding a cap across the power supply input but that didn't work. Any one know how to get rid of this noise. A single arduino
can take the place of a lot of ic chips and wiring so would be great to use one.
Thanks.

even if there's nothing else connected to the arduino.

What is connected to the Arduino? Do you have an amp connected to an Arduino output?

The Arduino doesn't have a true analog output. Are you using PWM? PWM tends to be noisy, especially at the default PWM frequency of around 400Hz.

DVddoug, nothing is connected to the arduino except +12v.d.c into voltage in and ground. I put the arduino on a breadboard the has a tremelo curcuit, so the amp is pluged into the tremolo out. The arduino is just sitting there on the bread board but it induces a loud hiss noise in the tremolo circuit. Adjusting the tremolo makes no diffrence in the arduino hiss. The usb is not connected to the arduino. The is no hiss when I remove the arduino.

I put the arduino on a breadboard the has a tremelo curcuit, so the amp is pluged into the tremolo out. T

So what is this tremelo circuit?

Basically the Arduino like any other micro computer kicks out noise. If there is nothing connected to the tremelo circuit then it will pick up this noise.
To stop an audio circuit picking up noise it has to have a low impedance input of some sort.

Will a 1K from input to ground stop the noise?