Soundflowewr is a third-party app that appeared on the scene somewhere around or just after Maverick. It expanded the versatility of Mac's native sound app and allowed interfacaing with some TPAs. I did not DL it on my own initiative but it came bundled or liked with an app I was testing - I'm not sure which at this stage. It seemed stable until I upgraded to Sierra or High Sierra. That is when the crackling began. Apple pushed out an update this past summer and that was the start of my woes until I disabled Soundflower. That's about all I can add. All I know is that it cured my "right speaker static and crackle." Again, with the iPhone X's approrach to stereo and the crackle coming from only one speaker (is it "right channel"???) I suspect the origin may be software.