What errors in a pcb layout for audio circuit cause radio reception?

I have a pcb designed and built that is for a synthesizer voltage controlled low pass filter. The circuit works perfectly (all the controls, i/o jacks etc.) except for one problem: when I have nothing plugged into it (no audio source being filtered) I can hear a lot of radio noise. When I move one of the knobs it is changing the radio blips (almost like tuning).

What are common errors on a pcb layout or circuit design that would cause it to act like a radio tuner? ground loops? high impedence amp inputs?

If the circuit is clipping then the distortion harmonics might go up as high as radio frequencies. A simple RC lowpass filer on the output might fix it.

The circuit might be oscillating at a radio frequency because an input wire or ground might be too close to an output wire or ground.

audioguru said:

If the circuit is clipping then the distortion harmonics might go up as high as radio frequencies. A simple RC lowpass filer on the output might fix it.

The circuit might be oscillating at a radio frequency because an input wire or ground might be too close to an output wire or ground.

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Both the things you mentioned would explain why the circuit would work as a radio transmitter (=RFI source), but not as a radio receiver, which I believe is what the O.P. is actually asking about.

problem solved! I was using ssm2164 quad vca ICs and I forgot to include the mandatory 500ohm+560p RC filter on the input of each VCA. Once I added those all noise eradicated.