@Tilo > Four possible causes for the pops/crackes:
1) Static or shorting on one of your devices (unlikely).
2) The audio buffer is underrunning; increase the size to try and reduce that from occurring.
3) The Intel Turbo Boost is kicking in; setting the max CPU to 99% in the power settings will eliminate that potential issue.
4) If the crackle only occurs when your power cable is connected to your laptop, that indicates a poor quality shielding between the charging circuit and other components in the computer, thus noise is heard and the recommendation there is to either not use the power to charge while DJing, or to use a USB isolator like this (not guaranteed, but certainly fixes a lot of similar ground loop issues).