Intermittent Front End Chattering/Shaking

My 99 Grand Am recently developed a problem. After a few miles of driving on the highway, the front end chatters and shakes the steering wheel, sometimes severely if the brakes are applied. It then disappears for up to a week, and then comes back. Have had the tires rotated and balanced. Alignment is next, although I doubt that is the problem since it is not consistent. New rotors and brakes recently. Any ideas?

the rotor backings need to be real clean and smoothed and the same around lug bolts , this prevents vibrations. also you may have a brake piston burned out or sticky. Also , the inner part of the rims gotta be clean all around for an even balanced ride. New brakes can warp new rotors when used agressively at the brake in period , if that is the problem get your rotors machined on a lathe.