There is a metal rubbing metal sound coming from the rear of my 2006 Hyundai Sonata. It happened with a cold start, and it was cold outside, but we were not pressing on the brakes. We backed up, changed gears and moved forward, and it sounded like metal rubbing metal. I thought it was the rear brakes, but it continued whether we stepped on the brake, took our foot of the brake, accelerated, or just coasted. It finally stopped on its own after we drove about 5 minutes. Do you know what that could be?