I've got an '05 base model sedan, so drums in the rear, an disks in the front. 12k miles. Today for the first time I hear a light thump, thump, repeticious noise from the drivers front wheel. One thump per wheel revolution. This is noticable at speeds above 25 mph. This happens with no brake application and is consistant. There is no felt wobble with or without applying brakes. Is this typical of warped rotors on Cobalts? Other cars I've had with warped rotors only make noise or wobble when the brake is applied. I thought warped rotors were less prevelent on Cobalts with 15" wheels?? I tightened the crappy hub caps, not the problem. Any ideas, or experience similar to mine?