Whenever I have 2 cables plugged into my AB/Y pedal, I get a hum like noise through a couple amps, and a crackling type sound through another. If I unplug one cable, sound is crystal clear. I thought it was the power to light the LEDs, but it is only when 2 cables are plugged in. I have tried spraying some cleaner into the contacts and it makes no difference. Any ideas?