Hi Laszlo,
I think I identified the problem. It is probably faulty USB cable that was supplied with the unit. I am not 100% sure yet as I don’t have a spare USB cable at the place I am right now. But, I have a short quality USB extension connector. When I plug that black usb cable into that extension and then into computer the crackles go away and the sound is clear. Not really sure what the miracle this connector do, but the result is clear sound 🙂