When I'm driving on the freeway by myself and I look to the right I see the passenger seat shaking a lot, it doesn't make a noise but it is a cause for concern. I have 20in rims on it with some decent tires and the dealer adjusted once before, but I got into a little fender bender and I think the body shop messed that up...

So does your passenger seat shake ridiculously?

Try moving the passenger seat. I saw my passenger seat back shaking a little bit once. I moved the seat back to a slightly more reclined position and it hasn't done it since.
Do you feel any vibration in your steering wheel?

I, too, noticed my passenger seat shaking pretty violently on the freeway on many occasions...

Aeson - I will try your tip next time I see the seat shaking.

I do feel a small vibration in the steering wheel but its hard to tell if it is the freeway or the car because it varies on different roads. I think I'm going to try adjusting the seat, and taking it in to the dealer.