Could it possibly be the road itself? I know with my 2007 Sierra that supposedly doesn't have this problem, I'll get different vibrations transferred though the pedals or into the empty seats next to me when driving on different roads, such as new asphalt vs old asphalt, or new concrete vs old concrete, etc. Just one thing to possibly pay attention to when noticing the vibrations or not.
Yeah man that sucks. Somebody at my school thinks the bed of my truck is a trashcan because I keep finding their Chic-fil-a bags and half empty drink cups when I walk back to my truck after rugby practice.