Warped rotors are caused by heat. It is very common. What happens is the rotor (which is the round plate behind the tire) gets hot and is no longer true. It wobbles a little. It could be ever so slight and not seen by the naked eye. Even if it was bad, you wouldn't be able to see it. There are two options that can be done. If the present rotor is still thick enough to be cut, it can be trued up on a lathe. If they are too thin to cut, they would need replaced.
As far as what you mentioned, it sounds like you are looking at the rotors. It is common for them to have scratches in them just from normal use. Yes, what you said makes total sense.
As far as your mechanic, I would think he would question the rotors. Based on what you have told me, (the noise stops when you hit the brakes) tells me that the problem is brake related. If a rotor is warped, it could be rubbing against the brake shoes at its high point and then be away from the rotor on its low point. Thus, you hear the sound.
Think about it. The sound speeds up when you speed the car up. Therefore, it has to be something turning at the speed you are going.
Jen, I am not there to actually hear it, so at best, I can hope I'm giving you good info about your problem. Hang in there and let me know if you are able to do the test I described. Or, call your mechanic and ask if he can cut the rotors on the rear of the vehicle. It is usually a cheap job to do. I live in PA and would estimate 10.00 a rotor to cut and 30 minutes labor. It may be different based on where you live.
Let me know what you find. I want to get this fixed for you. Let me know if you have other questions.
Monday, July 29th, 2013 AT 7:09 PM