normal (?) vibration (resonance?)

recently bought a 2011 w/ 105,000 miles. all seems normal but it gets a slight vibration between 55 and 75 mph which is more pronounced at 72. at 78-80 and above it's smooths out. feels like maybe the entire chassis (body) is resonating with the road surface and maybe it's common or frequent with the model. don't find complaints in the chats so am looking for other's observations. tires have been rotated and balanced.

 

thanks, Eagleray--responses to your questions: put 6,000 miles on since purchase; vibration (sound) been there all along but seemed kinda normal; vibration is mostly noise, like subsonic (akin to the vibration when you open a window at 50 mph); i thought wheels are supposed to warm up at speed, so yes tires are warm; no accidents.