If you want to have it bounce while something is happening and then stop it, you could use setInterval
var interval = setInterval(function(){
jQuery('#someId').effect('bounce', {times: 5}, 300);
}, 500); // every half second
// Do some stuff to load up your site;
clearInterval(interval); // Stop the bounce interval
You may want to adjust the times
parameter and the delay
to meet your needs and effect.