It's probably memory. Your imagination is a very strong thing and it will recreate the sounds in your head from time to time. Since you probably play Blockland a lot, you must have a very vivid memory of these things. And I kind of like this topic because I always find it weird how your not really hearing things it's just in your head, like when you get a song stuck in your head, you are not really hearing it in reality you just think you are.