I have a 2015 Optima with 69k miles. Just recently I started getting a vibration while driving at 65 mph or faster. When it first began, I noticed that the brake peddle would also vibrate/pulsate when braking. I attributed it to a rotor/brake issue. I took it to my mechanic and had him replace the front rotors and brake pads. This fixed the problem for a few hundred miles. Then once I hit 65-75 mph I began to notice a vibration coming from the rear. The vibration became so sever that the whole car would shake. I took it back to my mechanic and he did the rear brakes. The shake did not go away. My mechanic checked all the brakes again, the front axles, the transmission and could not locate the problem. I had the tires checked and balanced and the problem continues. The car is now undriveable on the highway. Any assistance in making my car driveable again would be greatly appreciated.