In the past when the car is slowed to 80 it would go away. This has happened 4 times. When it happened on the weekend it didn't stop at 70-80. This is my wife's car and I haven't been in it when it's happened, so I'm sorry if I don't know all the answers. She has said that the handbrake wasn't on. She called me when it wouldn't go away because she was scared that car was going to fall apart and her voice was shakey on the phone from the shudder, so it was bad. I told her to pull off the road and turn the car off and on. This is the only time she has had to stop. The Ford dealer said the first time we had it in, that this could be air in the power steering fluid. Is this possible?