50 Hz Hum with guitar lead

I am getting 50hz hum whenever I plug a cable into the input of the PISound. With and without a guitar on the other end of it

What might be the cause of this?

I have a guitar amplifier here that does not have that problem so it is not the lead.

What sort of power supply are you using in this test?

The Raspberry Pi supply.

Is there anything else connected to the system, like some USB devices? Is the output connected? If it is, could you check if the hum is apparent in recorded audio when only the power supply and the cable to the input is connected?

Running it off a battery get the hum

Can record it using audacity

Nothing else connected except head phones

Home not apparent when I turn off mod-host. It is a mod-host plugin.

http://guitarix.sourceforge.net/plugins/gx_aclipper_#aclipper to be exact.

Does this mean the hum is audible only when the plugin is in the pedalboard?

yes. I am using mod-host on its own

Does the hum appear if simply connecting input to output, to bypass processing, using jack_connect system:capture_1 system:playback_1 and the same using _2?