the gr 20 is powering the gk pickup  so its probably sending a bit of  power to the variax   throughthe  jumper cable also the pod is powering the variav through the rj45 cable.  your best bet is to   make up a small replacement cable from the  gk  with a stereo end on the  1/4 inch end   and leave the center section disconnected. i have that same gr 20  and the gk  but im putting  the gk kit in  nistead of the clamp on pickup so ill probably run into the  same  problem.