What kind of rattling noise? Have you gotten underneath to look at the heat shields to make sure taht they haven't come loose fallen off? On mine the bottom heat shield did fall off. So it will rattle on occasion. To fix it, all I need to do is get underneath and clip off the bracket that used to hold the heat shield. Its not a big deal to drive without the bottom heatshield. That would be my first reccomendation. Much cheaper and easier to fix
Afther that, just keep looking around to see what may be the cause.