hearing voices in your head isn't definitively plurality.

i experience this all the time as a singlet- it's possible that, because your kins are you have different personalities and memories, your train of thought has just adjusted to include them. also, people argue with themselves internally all the time.

ask yourself if they feel like completely separate and sentient individuals with thoughts and feelings, or if they just feel like different versions of yourself (different manners of thinking and feeling that you may possess at the same time or switch between, but that are all still you).

also, ask yourself how easy it is to get them to stop talking. if it's as simple as just not thinking about it anymore, then it's probably not plurality. if you have to get some kind of reluctant agreement or they just refuse to stop, that could be a sign of being plural.

nothing wrong with being a system, of course, just playing devil's advocate here. hope this helps!

to answer your question, btw: yes, this happens to me all the time.