I can't isolate exactly what circumstances cause this (it might be after a restart it happens only once.. I'm not totally sure), but on occaision (and with high annoyance), iTunes starts when I unplug my headphones. I don't ever use iTunes, and I don't have iTunes set to open on start.
I have an external monitor connected, so perhaps it has something to do with this?
MacOS 10.13.6, updates completed.