When it comes to vibrations think in terms of rotating parts. Nonroating cars may transmit vibrations, but they are not the cause. Rear end suspension problems are known to cause klunks, thumping, or rear end steer. If the vibration is much faster than the wheels, its likely the driveshaft. Then check flex discs (loose bolts are possibility), center support bearing & mount. Freestylers experience is similiar to mine. However, I did not rebuilt the suspension twice to solve vibrations, so I was not disappointed that it did not.