I'm not saying this is your problem, but I would seriously consider having the wheels tested for trueness and also that the spokes are the same. I drove myself crazy trying to figure out the problem on my Jetta. I rotated the wheels myself until I found where it vibrated the worst. I then had that wheel checked for true. Radially it was fine, when the tech put the laser on the spokes he found the problem. The bad wheel wasn't that noticeable on the rear, but stood out like a sore thumb on the front. I know how frustrating this can be from personal experience.
This is the actual wheel that the tech found to be out of whack. The laser showed the circled spoke to be machined out of tolerance with the others causing the vibration. Again, this may not be your problem, but it doesn't hurt to check.
