So I have a 2006 Pontiac G6 83,000 miles on it. When I have been going highway speeds and I start to brake to slow down, my car vibrates. I replaced the front brakes and had the rotors shaved about 20,000 miles ago. I put top of the line ceramic brake pads on because I found out the semi-metallic pads I had put on previously were crap (thank you autozone for recommending that junk). I still have the semi-metallic pads on the back because I have not had a need to replace them quite yet. It feels like the vibration is coming from the front of my car and my first thought was the rotors were getting warped but I have a hard time believing that since I just had the work done 20,000 miles ago. Anyone have any thoughts?