I recently listened to an audiobook called A Long Walk to Water. There was this strange echo effect when a character was thinking. (At least, I think that's what is going on.) I also listened to an audiobook called Shatter Me, where I eventually figured out that a recurring sound effect was words being crossed out.

What do you think about sound effects in audiobooks? To me, it starts to verge into a radio play. I kinda just want someone to read me the book. But then again, I enjoy when a narrator does different voices really well, so maybe I just contradicted myself. :)