RE: Dell XPS 15 9550 Crackling Noise coming from speakers when plugging and un plugging power supply.
Forgive me if I'm putting this in the wrong place.
While it isn't a fix, it might help diagnose the issue as this seems to be with Windows. Had 3 9550's and on this 3rd one, braved using Linux as my primary OS - and hey presto, no audio issues! Audio actually sounds decent too. All 3 laptops do this under Windows, but under Ubuntu 16.04.1 LTS, nothing!