I just got a Fender 68 Custom Twin Reverb that I would like to integrate into my PBC pedalboard setup. I tried using one of the function switch connectors on the PBC to control the amps Reverb and Tremolo. On the amp side is a regular TRS jack and the footswitch that comes with the amp is really just two latching switches shorting tip or ring to ground. When I use the footswitch everything works just fine but when I use the PBC function switch I get a really loud hum when one or both of the switches are open. If both switches are closed (Reverb and Tremolo are on) the hum is gone. This happens even when the volumes on both channels are all the way down. Any ideas what could be causing this and how to fix it?