Really?! That is fascinating to me. I am 100% language on the inside.
Personally, like codingdave, my "milk voice" is my own voice. I can "hear" my voice, with texture, inflection, and everything, as if I were reading my thoughts out loud. The milk voice doesn't have to be my own; I can vividly imagine the voice of anyone else I've heard. I have often wondered about that; how is it that with so little sample data (hearing someone talk for only a few seconds) I'm able to imagine them saying _anything_, with any inflection?