Puzzle - who's got an answer?

[clipless bumper]

I don't know if you read my 'small projects' thread - but I thought my battery switch mod had screwed up my Beano Boost.
Turned out to have been a bad cable - which really confused me cause I had been troubleshooting two pedals, and it only started causing a problem with the second one (Beano)

So tonight I plugged the same cord back in to my pedal board to see if it was truly shot, or what.

Worked great! Go figure. No noise, Beano on, Beano off. Played a while, Surface, Aquavibe on/off, using different boosts, etc. - no problems.

Then, I happened to turn off all the pedals in front of the Beano (it's 4th in line - Aquavibe>CC Hybrid>Sunface>Beano) and there was the loud obnoxious hum!!

I suspect the cable is open from sleeve to sleeve (no ground connection), but don't have a multi-meter to confirm this.

In any case - why would Beano hum loudly ONLY when no pedal is turned on in front of it?
If it's a bad cable, why does it only affect the Beano?

All pedals are true bypass, the CC Hybrid is positive ground. Sunface and Beano run off batteries, both of the other two run off isolated outputs on my Iso5.

Explanations?
Theories?
Guesses?

[Tortuga]

Is the Beano a positive ground chassis like the old Rangemasters? I wonder if it has something to do with that? Have you tried rearranging it so the Beano is first, just for shits & grins?

[clipless bumper]

yeah - the beano was first when I was troubleshooting it - it was the only pedal in the chain at that time.
it's only when they previous pedals are OFF that it hums - since they are all true-bypass, it's like they essentially aren't even in the circuit at that point.

And the beano and sunface both use NKT275's - neither of them is positive ground.
The only pedal I have that is - is the CC Hybrid.
I had thought that may have had something to do with it too - but doesn't matter if its there or not - the beano hums, unless ANY pedal is on before it (with the f'd cable only coming from the guitar - no other cables do it).

[Tortuga]