If the tire is indeed in balance, then you have either one that is out-of-round, or that the tread is not on straight. Tread being out of alignment is less likely than the tire being out of round, but both conditions are known. Unfortunately, I have had them both in the past. If it is out of round, it can be trued up. If the tread is out of alignment, it must be replaced.
If you can jack the tire up off the ground, You can get a fair idea by placing an object near the center of the tread, and spinning the tire. Watch the distance between the object and the tread. If you see this distance change, the tire is out of round.
Now place the object next to the outside edge of the tread where it meets the sidewall. Spin the tire and watch the tread alignment while looking from the front of the tire. You will know if the tread is out of alignment very quickly.
If both these test show nothing wrong, then place the tire in any position you wish, hold it in place, then turn it loose. Does it stay where you placed it? If it rotates, it is out of balance. If it does not move, then move the top of the tire to the 3-O'Clock position and see if it moves. If it does not, move it to the 6-O'Clock position.
If none of these test show any problem, well, perhaps you should have the front end alignment checked along with the steering linkage.