We sailed on Mercury out of San Francisco for an 8 day cruise on 3/13/2004. We did not notice any vibration at all. However, our last evening at dinner as the ship was dashing towards San Francisco, we were encountering the usual swells which on gets along the California coast, and with a table just one table from the rear windows, you could see that the stern was moving up and down about 15 to 20 feet.
Our only problem on this cruise was noise at night coming from activity in the hot dog and hamburger stand which was right above our suite. [We were in RS1054] For some reason they were working above us in the middle of the night, and it sounded like they were rolling bowling balls along the deck. Guest Relations was very good in trying to eliminate the activity or at least have them do so quietly.