Funky random shuttering in the front end of a 96 jeep cherokee


At random times while moving the front end of my girlfriends jeep cherokee will shake violently. There does not appear to be any conection with braking, turning, acceleration. Unsucessful repairs so far include new rotors, new shocks, balancing of the tires, new sway bar tie rods. I am completely stumped. It does not happen all the time just every now and then the front end will just go crazy with an epileptic seisure that will last a few seconds then dissapear and drive perfectly fine.