If you have musictracker set to auto-detect, it will periodically run 'mocp
-Q' to see if moc is playing anything.
It seems this has the side-effect of starting a moc server process if one is
not already running. I don't know if there is any way to avoid this behaviour.
If this really bothers you and you don't use moc, you could either configure
musictracker for the specific player you do use, or uninstall moc :-)