Sounds to me like maybe a belt has broken in one of your tires. Having the tire dismounted, turned and remounted will help lower the amount of the weights needed to balance it, but if it is a problem with the tire, or the wheel, the balancer will not pick that up. Only if a wheel is bent badly will the balancer pick up on it. I spin the wheel on the balancer before I balance it, that way I can look at it to see if it is bent or not, if it is bent I will let the customer know about it, then mount that wheel on the back and recommend replacing that rim before it tears up the tire. if it is a problem with the tire, rub your hand over the tire, feel for any low or high spots, if you find any, replace the tire, if that doesn't fix the problem you might want to have your suspension checked.
Hope this helps a litttle... TJ
