Crackling when recording in Audacity
I’ve never had an issue recording in Audacity. Tonight I feel like throwing my fucking computer out the window. I’m not redlining at all. I get crackling in the last two tracks of my mix. Wtf?! 
Check the input gain for the recording in Audacity
Your gains may be good on your mixer, but Audacity’s may be too hot.
If it’s only the last couple of tracks in an otherwise fine sounding mix, maybe your CPU is getting too hot towards the end?
Lots of tricks to keep it cool - try propping your laptop up at the rear to get some cool air circulation going near your fans/vents…
Ended up just recording the mix in Traktor. Worked out ok. Still gonna try and figure out what happened in Audacity though. 
Check you ASIO/Core Audio Buffer size and sample rates