No one here has mentioned that this shake could be causeed by a slipped radial belt in a front tire. This is not unusual. The tire could have been defective new or a pot hole or a curb hit can shift a radial tire belt. They will feel like a bent wheel. If they are bad enough you can jack up the front end and spin the tire and see a shift (jog) in the thread pattern when the shift in the belt comes arround.