At 55+ mph it feels like my driver side tire is hopping or has a shimmy. 2011 HHR. WTF? I just replaced the tie rod ends, struts and sway bar rods.

 

Any bulge anywhere on tire?side or tread, possible broken belt,what about water in tire,some air compressors,not drained properly,can move quite a bit of water

 

I rotated the tires, front to back and it calmed down up front, now the butt's waggin. new tires in my future.

 

Is it possible that the new front end parts had moved the sweet spot of the front tire, and some cupped tread is now in contact with the road. Moving to the back just moves the noise....lol
I had this happen to a geo metro we owned ages ago. I did not rotate the tires often enough.
If you do get new tires, rotate them more often. I was told every 3000 miles on the all weather nokians I bought.

 

One of our tires causes a slight vibration, turns out the wheel is slightly bent. Not bad enough to replace though.