I had a newer tire that caused that, something split/separated inside.
It could be balanced fine, but when under weight pressure you noticed a "bump" while at very low speeds, like you were running over a small rock off-center repeatedly, but it would be fine at higher speed and then caused a shake at highway speeds.
Rotate tires back to front and see if it you can feel it more or less in the steering wheel.
Road force balancing will almost always detect a "bad" tire.
Last edited by RonD; 07-21-2016 at 10:59 AM.