Weird Happenings

Okay, so every Friday when I'm walking back from Cooper, my backpack makes the strangest noise. It's only on Fridays! It sounds like a mix between a dog barking and an owl hooting.  I have three explanations for it. One: The books that I have in my bag move strangely and make that noise. Two: the combination of the books, the wind, and the way I walk cause the sound. Three: an animal jumps into my bag every Friday sometime during class. I always want to slap my bag and see what's going on in there, but I would look like an idiot! I have no idea how to silence the noise, but it makes me feel self-conscious. I'm worried that people are going to walk next to me, hear it, and ask their friends, "What is that noise coming from that strange girl?" And I have no answer!!! Then after a while, it just gets annoying, and I can't wait to take off the bag and drop it on the ground.