low level noise issue power supply or ground noise

Hi Guys,

it sound like some laptops connected to mixer. Not only noise some other higher working noises are audible at very high level. So if you record a bass for example afterwards compressed and maybe a limiter at the master it comes thru especially in silence between the notes.
I try to disconnect the usb cable, other cables also i try the old trick, that is dangerous. Nothing helps..

regards,

Marc