After checking out compatibility with all my apps and gear, I updated by MacBook Pro to El Capitan (10.11.4) and all my NI products just to hear that my Audio 2 DJ (Mk I) outputs digitally distorted sound on both outputs when using Traktor (2.10.2 9) - I have updated to the latest hardware driver (v2.80) and all other NI software is up to date. - Changing output levels doesn't reduce the crackles at all. - Neither does changing the latency value. - Neither does switching the USB cable. - What's interesting though is that when I open the preferences window in Traktor, the crackling stops WHILE IT OPENS. When the prefs are open, the crackles continue. - It's a MBP mid-2009 with enough RAM, hard drive space etc. – I have an RME interface in use with Ableton and that works perfectly fine - it's clearly the NI driver! Does anyone have similar issues? UPDATE: I checked with other apps and playing tunes directly from the Finder, with no distortion at all. This suggests it has nothing to do with the Audio 2 DJ driver, but only with Traktor 2.10.2.