Volume control dependent frequency shifting

[Unlikekurt]

I recently completed a RAT build.  One of very many at this point.
However, this time there's a bit of something strange happening.

At extreme setting I can pitch bend the "tone" of the feedback with either the rat's volume pot or the guitar's volume pot.
I've even scoped it. 

Here's the scenario:

I'm cascading one rat into another (as i said i've got a pile of them).

Rat1 into Rat2 into scope

Rat 3 into Rat4 (the one that shows the issue) into scope

I set the pairs for the same settings (even checked them with a meter).
With a guitar plugged in and resting silently without any string vibration, or just with an open cable at the input I see the same result
There's a square wave on the output and in scenario one if i adjust the volume control of Rat2 i see the waveform decrease in amplitude but it does not change in frequency (x axis). 
With the second pair set up i can most definitely see the waveform frequency get larger and smaller again as i turn the volume pot down from the maximum setting.  If i keep the volume control at maximum and make the same sweep with the guitar volume pot i also see the same thing.

Can someone possibly point me in a direction of understanding and possibly amending?

Thanks!

[GibsonGM]

2 second analysis: you have so much gain going on with the cascaded Rats, and enough phase shift with all the C's in the path, that you're "violating" some rules about how to keep a stable signal...in essence, it's an oscillator.   ANYTHING can make it start...random noise...the guitar and cable are just helping it along.

Your tweaking the R happens to modify the frequency it/they are oscillating at. 

Why say Rat 4 "has the issue"?  Doesn't do it on its own, right?   If you change order, and put Rat 1 in the 4 spot, does it still do it?  If not, I'd say just a consequence of what I described above.

Remedy?   Don't run 4 Rats into each other   Or, look at the schematics and remove unnecessary C's, read up on some feedback theory about how to stabilize things like this...but I wouldn't expect magical results...