I bought this cable at Best Buy and it says its directional. But I could not find any arrows or markings of any kind. Does it matter which way the cable is installed. I hear a slight hum coming out of my PB12 when there is absolute silence in the room. Do I have the cable installed or is this little bit of humming normal? I dont want to reverse the cable if I dont have to, major hassle because of my setup. Thanks to all who reply.