Hi Dale
I have been around these bike motors since 04 and have been on every motorbike forum I could find . This topic has come up several times . My conclusion from all I have read is that the motors have to be attached to the frame as rigidly as possible . This might involve filing the imperfections from the mount to make an even better contact . If you give these motors a chance to move , they will . They would only vibrate more with rubber mounts . ......... D.J.