Originally Posted by mm43
Potential noise culprits are the Zener diode . . .
Sorry, incorrect. Zener diodes are used in noise generators because they have a broad spectrum, not because they produce any significant amount of noise. In one circuit for a noise generator the zener is followed by +40dB of broadband gain and the output noise is still very low, about -50dBm. A great many electronic components produce noise, this is either specified in the data sheet or easily calculable from the component value. But none are in a range which would produce radio interference when properly designed and packaged. And, as Murphy has pointed out, a constant noise source would not interfere equally with nearby and distant signals. So please, let's put this one to bed. Thanks.