Reply to Brand new S4, but no sound from left with monitor output

After two years with a Numark Mixtrack Pro, I went to the next level with an S4. I recieved it yesterday. I download drivers, launch Traktor, set the outputs with the S4. Now, I am ready to play with. Put my headphones in the unit, plug my PA behind... And then, I notice I have no sound from the left in my headphone. I try an other pair, same problem. I try to reverse outputs in software (monitor used as main, and main used as monitor). Same problem, apparently this is not a software problem. I try with Ableton live just to be sure: same problem. When having full volume with the knob and not playing anything, I have a little ''psshhhhhh'' coming from left (the side not working), but not from the other side. That's weird
I sent a ticket to NI custommer support, waiting for a answer.
And today, I tried on an other computer, same problem.
I am very disapointed. I hope I won't have to send it back, because I am having fun with it. The unit is brand new, don't they have quality control procedures at NI?