I'm literally having EXACTLY the same problem. It's definitely the computer (not sure whether software or hardware) itself because this occurs for me without any external connections (headphones straight into the built in port and no MIDI devices or audio interfaces). I don't have a ridiculous amount of audio processing going on and my session only ever has about 10 tracks with MIDI and a couple of buses functioning at the same time, and it still happens even with the buffer size at 1024. Whenever I make edits during playback my track stutters, crackles, and pops exactly like that and it generally occurs in different spots each time and sometimes plays back completely clean. My CPU doesn't appear to be anywhere near maxing out (though I'm still frustrated as it maxes out quite easily at a lower buffer size), but I do notice though that one of the CPU threads seems to be a lot higher than the others at times (though this doesn't always happen either). I'm honestly just going to take my Mac in to the Apple Store because I've tried everything and it's still an ongoing issue. Will update if I find the source of the problem.
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