Movie clip plays at various speeds?

this is my site…
now i made all the buttons flash with a tint effect on mouse over… the story button flashs normaly but as i work my way down to the links button the flashing on mouse over gets slower… and slows down the anim on the left(which have been loaded in to a empty movie clip)…it all works fine if i run the swf on my computer but once its on line its slowing down…my pc should have no probs running such basic animations.
what am i doing wrong