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Sounds like you need to bleed the brakes!
If you still have the book that came with car, look under lights in the service section.
Check for a disconnected wire connector, if not you have a broken wire.
More than likely you need new rotors. The ones you have probably have differing hardness spots causing chatter.
I experienced this once. I had to disconnect my battery and leave it alone while I had a cup of coffee. This allowed the computer to reset correcting problem.
You might want to check the wheel bearing hub . An easy test is to remove tire and rotate hub forward and backward. It should move freely in both directions.
Most often this is the exhaust baffle rattling. It goes away after a few moments after warmup.