Flash of Light is a mez/stun cast every 30 seconds. It has a casting time which means that Clerics and Paladins can stop the flash from going off. The split second that the Ghost starts to cast a spell, stun it. Sound of Resonance is fast enough to land before the ghost can get Flask of Light off. Paladin stun lines are probably faster casting than the Cleric's. You just have to hope that you do or fizz the spell or the Ghost resists it. This will help down these faster since you are not pinned down for 10 seconds.