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My Scion XA just started making a rattling sound. It sounds like it's coming from the front, near the driver side tire. I thought it was the brakes, but I also hear it when I'm not braking. There is no sound when the car is stopped or idling. Any ideas what this could be? I'm trying to get an idea of how serious the problem and what I should expect in terms of cost/time to repair it. Thank you!