This could be many things first of all! your lug nuts could be loose on your tires or tire your rim(s) could be bent or your Front or Rear axle could be bent and/or loose one of the vaccum lines has come out. Find it and put it back in.
Could be rotor "out of round" and needs to be re-surfaced or replaced. Possibly caused by over-tightening and not torquing upon installation. Could be a "frozen" brake caliper. That needs to be replaced