I tried to use an oscilloscope today to check the power rails. I check them on the 356 board, but the seemed fine and I could see any significant fluctuations.
I realize that when I unplug the VCA out connector or power input on the VCF board then the noise becomes much louder. So I was able to put the scope on the output and see what it looks like. It appears to be a constant frequency pulse wave with a small cycle length, like 5-10%. The noise doesn't go through the filter so it isn't oscillator bleed and it doesn't track the keyboard. The only thing that really affects it is moving the arp switches.
I've found the noise goes away completely if I unplug the arp connector from the 356 board, but if I unplug the same cable from the other end, the noise remains, but is reduced in volume. I checked the cable and it seems good.
So I am thinking that either there is something wrong with my 356 board that is causing this noise or perhaps their is an issue with the cable routing (perhaps maybe it shouldn't be bundled with a power cable or something).
Thanks,
Chase