Make a button shake/vibrate

Hi
This must be really mundane for you guys but im trying to create a button that vibrates/shakes when your mouse moves over it. I want to use actionscripting to do this.

Ive tried using

this._x = (Math.random()5)
this._y = (Math.random()
%)

but when i test it the button always jumps to the top right corner.

any help would be helpful