2003 Mazda Protege

I have a 2003 Mazda protege 5 and I have a little problem. It has 57,000. When I start the car in the cold and I drive it makes a rattleing noise (squeking) when I stop or slow RPMs. Then it goes away when I speed up. After the car warms up the whole rattleing goes away! Any ideas of what could the cause be?