I have experienced the same problem today while exploring potential connection setups with the KPA and other gear, namely a POD HD500 in this case.
I have tried:
Guitar -> KPA -> KPA Direct output -> Pod HD Guitar In -> Pod HD FX Send -> KPA Return Input.
I get some sort of faint crackling / hissing sound. It is there whatever the input volume as soon as there is the slightest guitar note going through the loop.
Tried ground lifts even if it was far fetched for that type of noise, didn't work.
After a while I just unplugged the FX Send from the Pod HD in frustration thinking it was coming from it. The other end still being plugged in the KPA Return Input.
I was surprised to still hear the crackling noise when I touched the tip of the cable with my finger... It made the usual feedback sound when grounding the cable or plugging it to something but the weird static sound was being generated at the same time... Odd. When there is no signal the crackling is not present. Only when a signal is present.
Hope they will find the problem without having me to send the unit back.