Balance perfect? What does that really mean? Are your weights stickon or normal weights on the lip of the wheel. Lip weighting preferred for best dynamic balance.

If it were me, I would find a shop that has a Hunter GSP9700 balancer.
Go to www.gsp9700.com and click locate a dealer tab.

Best system on the market. Good chance they will find the problem.
The new Bridgestone Turanza's I bought for my '97 S320 were alledgedly perfectly balanced at the place I bought the tires. I tried them for awhile. Took them to the shop with Hunter machine and, sure enough, slightly out of balance. Now they are perfect.

Steve