I had my front flex disk replaced a few months ago. Since then there has been a vibration in the driveline under medium to high load. The tech who installed it checked the driveline for play, looked at the rear flex disk and support bearing. All checked out. Installation was apparently correct as well. They changed out the transmission mount with my permission without any better results. Had another tech check it out and he checked the whole driveline and now suspects the flex disk that was changed is of a harder/stiffer material. I accepted it but am now wondering. Does anyone have thoughts on the problem and the theory of the cause. Is the difference between the front and rear flex (as the rear one was not changed and is technically apparently still good) possibly causing an imbalance? Does anyone think changing the rear flex disk to the same as the front will stabilize the drive shaft given that apparently everything else seems to be ok? Thanks.