I'm really sort of surprized to hear about so many rattles on new cars. I learned something the last time I bought a car, and that is to drive a used version of a car you are interested in. We drove 3 used Corolla's about a year old and one of them with 33K miles. All of them were still really tight, and non of them had any rattles.
A new corolla should be rattle free. I wouldn't except anything else. If you are worried about your dealer not being capable of fixing them problem, then you might want to find another dealer. I wouldn't wait too long tho because rattles are sort of a grey area because a user could be the cause.
If you want the rattles fixed under warranty, at least get a warranty ticket started. Even if they don't fix it the first time, you can have a record that the car had rattles at low milage. Later you can work with Toyota and find a solution on your time. I think it's important to get a record of a warranty problem as soon as a problem comes up.
I'm new to Toyota, but so far, I am having the best of luck with them. My car seems to have been delivered 99% perfect. Around 500 miles, I noticed that the driver seat seemed a little loose. It made a knocking/poping noise when I moved around. I took the car to the dealer and they didn't try and give me any crap about it being normal. They ordered a new seat track and they must not have dug far enough to find the problem. The ended up ordereing me a whole new seat, and gave me a loaner 05 Rolla CE that had 5 miles on. I hope my car will be ready today because I like the LE 5sp much better then the auto CE, but they are fixing the problem. I kindly told them I wanted the problem fixed the first try and they are not closing the ticket untill it is fixed.
It's my understanding that Corolla's are built in Canada and California. True? Mine was built in California. Where are the rattle ones being made?