For me they come out of nowhere. They don't have to be triggered by something and it's not in my own voice. It's usually not even the voice of someone I know personally, like someone I've never heard before. Yes, they are inside my head but it's not spawned from an logical train of thought.

I can usually tell the difference. Usually. Sometimes its just chatter that I can't even make out because it's SO many conversations going on at the same time that come from nowhere and I have NO way of shutting it off. If it's a regular thought then I can usually push past it and "shut it down".

The song getting stuck on loop, or replaying conversations is completely normal (I think). But I also think it's just a little worse for us because of a tendency to ruminate about things. But at the same time those things don't usually interfere with daily functioning. If anything... it gives me a soundtrack for the day... which for me personally I kind of enjoy. Unless it's a stupid song that I hate.

Edit: I should also add that 95% of the time they don't bother me all that much. When it wakes me up and keeps me awake at 3am is the only time it legitimately bothers me.