When driving the headlights shift up and down. (as if they are blinking) This is very noticeable at night and during the day, you can notice the reflection of the lights on the car in front of you. We have taken the car to two mechanics and a Ford Service center. No one has been able to resolve or pinpoint the problem, because it has never happened during servicing. The Ford dealership kept the car for 3 days and did not see the problem, however it does occur. I would appreciate any advice.