Background hiss Pioneer DDJ-FLX4

A fairly noticeable hiss is coming from my Pioneer DDJ-FLX4 board.  It is coming through both speaker channels.  I have all electrical sources plugged into a line conditioner.  The hiss is present when all volume and gain controls are at zero and no music is playing. I use the same speakers with other Pioneer boards and get no hiss.   PLEASE HELP!