Thanks for all the answers! I've never had this chance to hear about other people's before.

My voices have been really inconsistent, too. I think that when they first started, they were like a really faint radio. I don't know when the voices started so I'm not entirely sure. Then one day, I went to the doc's with an unrelated problem and got a bit snippy with him to turn off a radio that was bothering me - that wasn't really there.
That's when I started getting drugged against my will, "for the voices". Bizarrely, they were only loud and aggressive when I was willingly drugging myself; if I fought the doctors or the drugs then they were nice to me.
Now I'm off the drugs, I hear all kinds of voices. Some are annoying; some sing show tunes (also annoying!). Some narrate everything I do. Sometimes they talk to me, remind me about things I've forgotten to do. Last night, they were begging me to buy cow's milk (which I don't drink) and I had to talk them down :