I have a 2010 Mazda 3i Touring sedan (with manual transmission). I have a metalic rattle coming from the right rear of the car. After a number of visits to the dealer (including rear shock replacement), the problem turned out to be loose splash guard within the fuel tank. This seems to be a problem endemic to all of the newer models. Replacing it with another tank won't help since they all have this problem. Hope this helps for what it is worth.