I had bad vibration problems that I attributed to uneven (cupping) on the inner portion of some Bridgestone RE730's. This created annoying vibrations around 75mph. at any other speeds, there was either less or no vibrations. Unfortunately I drive 90% on the highway so it has made me very sensitive to this kind of problem. You might want to check whether all the blocks are smooth vs some higher than others....
I ended up shaving some of the blocks in order to reduce the vibration and avoid trashing the tires. I had noticed the same kind of pattern on a 944 when I went to do a driving course at Watkins Glen.
I was told a re-alignment would fix the problem. I am now running So-3s. I hope not to have the same problem.
