It's almost certainly warped rotors that are causing the problem. The first time around, it's always hard to tell what causes it. This sort of thing happens most often if you live in a mountainous area and use the brakes coming down mountain passes instead of relying on the drag from the engine. The other thing that can cause it is corrosion in the brake calipers. If the brake pistons aren't retracting properly into the caliper housings, then they will be binding slightly on the rotor when you're driving. Not enough to make any difference to the handling, but enough to overheat the rotors. The solution is one of two things. You can either get the rotors re-machined where they're placed in a machining tool that shaves off some of the metal around the face of the rotor to make sure both sides are parallel and flat again. The other option is to buy new rotors. Bear in mind that if you have them re-machined, they lose a lot of their heat capacity and its a lot easier to warp them again. It's also a lot easier to make a warped and re-machined rotor fail.