Vibration
 

At highway speeds I can feel a slight vibration. I can even see the passenger seat headrest vibrating a bit if nobody is in the car with me. It seems to me it's done this since new, and I thought it was just the roads, but my wife commented she felt it the other day.
It's tough to say if it changes with speed, It seems fairly constant. My first guesses would be tires or a driveline, but I wanted to see if this was something common that other had experienced.
Thanks in advance.

I've had flats and repaired rims so I know exactly what a poorly balances wheel can do to the headrest lol (Shaking). Start with getting the wheels checked and balanced if needed. These cars should have no shacking on the highway, not unless you are going over the speed rating of the tire. Every time I noticed my headrest shake, its always been a wheel balancing issue, suspension is stiff and I've had the balancing weights on my wheel just fall off since its just sticked up with adhesive.