My XC-40 developed a vibration under braking at highway speeds (above 45 mph) after about 9,000 miles. About half the miles on this car include mountain driving (I live in Colorado). The dealer replaced both front rotors under warranty: problem fixed, for now. I am wondering if this was a one-off issue or if this is a design flaw: are the brake rotors sturdy enough for extended mountain driving? I noticed when I use cruise control to maintain speed on long downhills, engine braking is often insufficient to maintain speed and is supplemented with extended automatic light appliaction of the brakes. I am wondering if this generates too much heat in the brakes and is part of the issue. Will post in this forum if the problem reappears. Has anyone else experienced this?