Magnum mount issue?

Someone tell me how a stationary item with no moving parts like a mount can cause a vibration. The mounts are supposed to isolate minor vibrations from rotating assemblies or from road vibration. Somewhere in your rotating assembly it is out of balance. I have solid mounts in my Valiant and do not have any vibration because everything is in balance. Why did you not have your balancer & flex plate balanced with your engine? Better go back to your engine guy.