1. Wheel not center on hub (centering rings may help)
2.. Warped rotor
3. Loose front end parts
4. Worn ball joints
5. Worn pitman & Idler arms
6. Worn die rod ends
7. Worn wheel bearings
8. Worn CV joints
Warped rotors can be caused by over torquing the lug nuts or by overheating the brakes. Have your front disc pads inspected and the rotors looked at. If the rotors are indeed warped, replaced the pads and have the rotors turned and trued. It can also be a loose wheel bearing, loose lug nuts, or a problem with the tires. Everything needs to be looked at. When the wheels are replaced make sure they use a torque wrench and torque them to factory specifications.