maybe Dolebludger or Don will chime in, think they have been on both ships...here is a recent post Dolebludger posted on CC about the vibration (none) on the cloud:

A good point has been raised, in that we have experienced vibration or shaking problems on all current RSSC ships except the Mariner. We found the Silver Cloud to be the most vibration-free ship we have cruised compared to RSSC and a number of other lines. That's a good thing. Further, we also like smaller ships (on RSSC, we favor the Paul Gauguin and the Navigator). r/wes