Congratulations and thanks to the MuseScore team. Moreover, it gives the possibility of using MuseScore with numerous third party software instruments. When composing and finely tuning the nuances of piano pieces, I used to export the score as a Midi file and then import it into Pianoteq. The MIDI-Output of MuseScore 2.2.1 is a big improvement. I solved the problem with the old MacBook Pro (15', end of 2008) by linking MuseScore to Pianoteq through the new MIDI-output of MuseScore 2.2.1 and it worked fine. Therefore, the crackling noises appeared specific to the old MacBook Pro. I tried MuseScore 2.2.1 with a MacBook Pro (13', end of 2011), 2.8 GHz, Intel Core i7, Mac OS 10.12.6 (Sierra) and it morked fine, without any crackling noise. However, when I moved to MuseScore 2.2.1, I had constant crackling noises during playback, except for the first one or two measures, with all instruments. I used MuseScore 2.1.0 without any problem with a MacBook Pro (15', end of 2008), 2.4 GHz Intel Core 2 Duo, Mac OS 10.7.5 (Lion).
About crackling noises with MuseScore 2.2.1