So I bought an M-Audio Uno USB-MIDI cable so that I could update my Peavey Vypyr to 1.70 firmware, and also to attach to my Digitech Whammy Pedal so that I could mess around with it in Cubase. However, as soon as my MIDI cabe plugs into the Whammy pedal, my amp just starts humming and buzzing. It's like a light phone static and it gets rather loud. I can lower the hum by turning down the gain, but I need the gain to be that certain level in order to get the same sound.

If the MIDI cable is unplugged, there is no problem at all. If I'm not playing, there's total and utter silence. Only when the MIDI cable is in the Whammy Pedal (and also in the computer) does the amp start to buzz. Any ideas? Is it something to do with the firmware?

UPDATE: I just noticed, it has something to do with the metal conduction of my pedal and the live wires connecting the amp to the pedal. As soon as I touch the metal part of my MIDI cable to the Whammy, I get the feedback from the Amp. The whammy doesn't even have to be on, I just need to touch the metal part of the MIDI cable. What do I do? Is this a defective MIDI cable? I'm using the Digitech 20th Anniversary Pedal, so the entire pedal is metal (I'm not sure if the regular one is metal as well, I'm just pointing this out in case).

Any fixes you could recommend?