So I was driving my Optima yesterday, and I kept hearing this "quacking" noise. In all my experience with cars I had never heard anything like this coming from a car before. I drove it for about 20 miles, wondering if maybe it was the tires, or maybe some kind of rubber rubbing against something, but there was no consistency to the noise. So, curiosity got the best of me, and I pulled over. Still quacking. So, it wasn't the tires. I popped the hood, and when I opened it, I very quickly discovered the problem. I met a duck, in my face, trying desperately to escape. After it flew away, I was in complete shock. It looked like it had nestled right in between the air-box and the battery. I still have no idea how it got in there. Must have been looking for some warmth, poor thing. So, just a warning, if anyone hears a duck noise coming from their engine bay - stop the car and release the duck.