Whenever I apply my brakes they sometimes make a horrible knocking sound. I had the brakes replaced, stopped it for a little while, then it came back. Although mechanics can hear it, they cannot figure out why it happens. Most told me that "cars sometimes make strange noises". It is not a strange noise, it is horrible. People riding in my car can hear it. I hate to even apply my brake, it makes me feel that I am doing something wrong.