Noise when the DJM is connected to the PC's USB

Hi,

I'm using the USB cable of my brand-new DJM-450 to record my sets through Rekordbox. I noticed that during the first hour of using the mixer, it is possible to hear some noises that come and go randomly. It's like a Gaiger meter noise. I don't know how to explain it better, it sounds like that. 
Whether I disconnect the USB cable, then the noise disappears. 

Do you have any idea of what could be the issue? I already measured the potential difference between the DJM ground and the (WINDOWS) PC's USB connector, and there is no difference.  

Hope you can help me.