With 9-12Kmiles on it, you will know if the car has this rattle problem or not. It seems when the car is over 5Kmiles and you don't have any problem with the transmission, you won't have it.So, the best way is to testdrive it before leasing it. Read the thread on the rattle problem, you will learn how to drive the car to hear if it has the problem (low speed on decceleration seems to be the first sign of having it).
And as you said, after you still have the warranty. A good thing would be to take an extended warranty to cover the whole leasing period (one more year to get to the 5 year lease).
