Motorized engine mounts

I have a 2004 Nissan Murano. There is an annoying sound when I start or stop the vehicle which is a whirring sound (which sounds like the noise that motorized antennas use to make when they went up and down). I found out that the sound is coming from a part located inside the motorized engine mounts. The Nissan dealership said that they can replace them to the tune of $1,200.00! I took it to a local auto shop and the mechanic said that he didn’t know much about motorized mounts, but said that the mounts look fine and that I didn’t neet to replace them. My question then is why are they motorized and what purpose do they serve? Should I be concerned about replacing them? The whirring sound doesn’t happen as often anymore, but the constant on/off noise was making me a little crazy. Interesting thing is that now that the annoying noise is seemingly easing up, the vehicle seems to be riding very rough. The final question is “to motorize or not to motorize”? Do thy serve a purpose?

The engine COULD be solidly mounted to the frame; but, it is rubber mounted to reduce vibrations from the engine to the car body (for the driver’s, and passengers comfort). Motorized motor mounts would be an attempt to further fine-tune the reduction of transmission of vibrations from the engine (and, transmissions).
Others have paid about $500 to have ONE motorized motor mount replaced. Yours may have only one motorized mount.