sway bar bushing
 

Wud worn sway bar bushes cause vibration in steering wheel at 80klm

That can do it, but my experience with similar issues leads me to believe its more of a tire balancing issue when it varies at high speeds. Usually if the bushings are worn the ride smooth out at speeds,you would hear more of a clickity clack noise when you turn the steering wheel. e.g leaving a parking space, etc.