Uneven brake wear on front

What is your question?

Just back from the brake shop. The noise that just started when I apply the brakes is coming from the front. They say that I have 40% more brake pad, but the pads are wearing uneven. This, they say, has caused the rotors to wear, and that they are too thin to turn. New pads and rotors=$400.00. Anyone know what causes this and is it covered under warranty? Mileage is 58,700.