mine had the vibe that your talking about and i just bought new tires the other day and it has stopped *knock on wood* so im thinking it was the tires that were bad

 

With most road force balancing they also find each tires "high spot" and each wheels "low spot" and match the two up to make a more even ride. I worked at a tire and wheel shop and doing this during a road force balancing makes a world of difference. If your local dealership doesn't offer this service it might be worth it to you to find a local service shop which offers this service. Tell them your problem to be sure that they will actually match up the high and low spots. If it is done correctly, you should notice a big difference. They will also verify whether the tire in question is out of round.