How long ago were the rotors "changed"? Were they replaced or resurfaced?the only thing thak causes the brake pedal to pulsate is when the rotors that are worn or where the inside and outside faces of the rotor are running out of round or out of parallel. That can be caused by rotors that are worn out of parallel or by bad wheel bearings in the hub that the rotors are mounted to. The problem with the wheel bearings would also show up when driving without the brakes applied so if you only get the pulsation and shaking on braking then the problem is with the brake rotors.Brake rotors can rust and cause this problem. They can also be 'warped' by wheels that are put on with uneven torque on the lug nuts. If you replaced the tires because of the vibration you can probably eliminate the torque on the wheel nuts as a cause because most tire shops torque the nuts to spec when they install the wheels and lug nuts.If the rotors were done recently I would recommend taking the car back to the shop that did the work and have them do a 'run-out' test to see if they rotor faces are out of parallel. It does happen where new parts are out of spec right out of the box. If its been a while they may have been worn out of round. If the rotors were machined rather than replaced they probably weren't machined properly and I would have them do it again.any reputable shop will stand behind their work. I'd take it back to the people who did the brake repairs and have them find out what they didn't do right or what went wrong since they worked on it. Again, if it only happens on braking its definitely a brake rotor problem with the front brakes.hope that helps