My head is constantly repeating certain song lyrics, proverbs, commercials, etc..
What's weird, is when someone says something even slightly similiar to a song lyric, or anything mentioned above, it creeps into my head.
For instance, if someone says "Oh, wow!", suddenly I say "ShamWow!".
I also repeat certain words when people speak to me. Most especially when they ask me a question. I suspect it serves two purposes. First, to allow me time to completely process what was asked. Secondly, to give me a few seconds to respond.
Example:
Friend - "Do you want to go to the store with me?"
Me - "Go to the store with you?"
Friend - "Yes, the store."
Me - "Sure."