What tire rating do you have? T? H? Z?

I had the same kind of problem( Yokohama Avid T4). Tire shop was balancing, balancing, balancing....and always had the same answer that maybe I was crazy and that their balancing machine was perfect.... They gave me 2 new tires, no fix. They looked at the car and said that it would be fix by changing the left driveshaft because they could see a little move(up and down) on it.

Finally went to an indy volvo guy who as soon as he drove the car said that I din't had the right tire rating for this car. He explained me that the machine they use for balancing cant see that kind of problem because the rotating speed is too low to make that kind of "deformation".

The tire shop sold me T rated tire and nothing less than H should be installed on this car if you drive over 70 mph. It seems that those tires(T rated) were too soft so they were "deforming" at high speed.

Changed for H rated(Potenza RE 950)and now the car is going great.