My '95 was doing this and I replaced the rotors. While doing this I cleaned a lot of corrosion off the hub where the rotor butts up against it. On my car it was so bad I had to knock out the wheel studs and use an air sander on the hub. (yankee car, road salt damage).
Anyway, if you have ANY corrosion, rust, dirt etc. on the hub face between it and the rotor it can cause the rotor to "wobble" and cause a vibration while braking.
