Richard,
You might want to use a 120 volt AC something from this page...
http://www.mcmaster.com/#electric-solenoids/=8cw86t
You can mount them on the table legs pushing down and one or two under the table for noise. Connect to a couple of non-dim circuits to energize as needed. You will need to make up an umbilical that can be easily plugged in between scene changes. For the ones mounted under the table, you might even add a chunk of metal or something else that the solenoid can bang against for extra effect.