I have a 2004 V6 and I've had it about a year, since it's my first car I've done most of the maintenance myself to learn more about my car. Everytime I stop from over 20 mph what I presume to be my cars brakes screech. If I lay off it stops and doesn't happen until the next time I brake over 20. I've changed all 4 pads and think it might be rotors. Any ideas?