Vibration or shake at highway speed?

[evan]

At highway speeds I now have a shake. I was going to call it a vibration but not like an electric razor, it’s slower than that and makes no sound. It makes the passenger seat shake when nobody’s in it and the steering wheel shake a bit. It’s not really bad, just annoying. The roads where I live are really crappy so I think it’s probably from a pothole I wasn’t able to avoid. It started about a week ago. Two days ago I rotated the tires but there was no change so I don’t think it’s a tire that’s out of balance.

Is there an easy diagnosis or are there too many possible problems? I’m going to take it in to the dealer but I wanted to try to get an idea of what it will take to fix it before they tell me it was $280 to change the headlight fluid.