On GM vehicles,they are required to used so much recycled steel. Since it rusts so quickly on body parts,they now use recycled steel on replaceable parts. On the rotors,they get a ridge on the outside causing vibration and noise, making you think the brakes are shot. Remedy? Can't remember brand,but one of the leading brake companies makes replacement rotors which are painted so they don't rust so quickly. Make sure you ask for the painted replacement ones. I did this in my 2004 Impala and it fixed the problem. I am getting a little vibration in the Cobalt now and will probably have to do it in time.
PHP:Can anyone tell me how to remove them?
They should just come off with some persuasion. Try a rubber hammer or regular hammer with a block of wood. They should and will sit firm on the axle. Don't be bashful loosening these up.
As for rotors, no dealer will you help you out here. They are wear items and sometimes will wear unevenly. Fortunately they're also pretty cheap and can be replaced easily and for not much. You can also have them machined to take out any warpage but make sure you get a good shop. They can come back worse than when they went in.