I can also totally relate. My 4.5yo dd not only talks, but sings all day. And it's that thing where she only knows one or two lines, and sings them over and over ad nauseam.
I was just reading a mindfulness post, and I wanted to respond (but didn't) that if I was mindful of my child all day, I'd have a headache after an hour. And that's not even mentioning my 2yo ds who loves to tell me things, but isn't always very clear, so it takes some brain strain to satisfy him that I know what he's talking about.
I think they're just sorting stuff out in their heads, and it just comes out their mouths!