Toyota Repair: wheel roters, metallic content, roters

Question
what are roters, and when they make noises when you stop your car, what can be done about them, and how dangerous is it to continue to drive it?
I have a 2003 Avalon, and it has been doing it since the car was 6 m0nths old. The dealer can never hear the noise,because I have to drive a good distance to get there, and when the wheels get hot, you can't hear it.

Answer
A groaning type of noise is common it's due to the high metallic content of the brake pads, not too much can be done exept replace the brake pads and resurface the rotors and making sure that all the anti-squeek shims and hardware are installed, I checked today on toyota's website and there are no service bulletins issued.