Hi. I connected a U6 to a new PC and notice that I am getting negative voltage readings despite no channels being connected. The voltage reading increases with channel number by about 1.1 volt. If I short circuit between GND and any AIN I get a reading of 0. I have used this device several times before, and seem to remember that in a disconnected state the channels read approximately 0 volts. Should I be concerned or just carry on?