Krankosaurus dist gain pot crackles w/boost on, even if dist is not connected

[Mad Dave]

Both channels (distortion & boost) work fine. I had wired it w/the boost chan in front of the dist (w/bypass switch for each chan), but noticed that if the boost was on, the distortion gain pot crackled when turned. (Though at a substantially lower level than when that particular channel is active.)

So now I've completely removed the dist section from the signal path, but the same thing occurs. Is this normal? I understand that the gain pot adjusts the transistor bias, but these are two totally separate circuits. Should there be interaction?

Also, If I touch the open input lead of the dist chan, I induce a hum into the boost chan. Is there some leakage here? Again, these are two totally separate circuits.

BTW, if hook up the dist chan, leaving the boost chan disconnected, I don't get the same things happening.

Schematic and layout PDF attached.