well you can crank your motor and listen to the front of the motor, if you hear or see it moving chances are its bad. and yes to change it you would need to remove the belt and the 4 bolts holding the pully on, the harmonic balancer would need to be removed with a harmonic balancer puller... http://shop.advanceautoparts.com/webapp/wcs/stores/servlet/product_13-Piece-Harmonic-Balancer-Puller-Performance-Tools_25989081-P_N3491_T|GRP2083____
but chances are its something with the drive train, if it was the balancer chances are it would be more like a knock and it would do it all the time