Well it is the most powerful healing mantra and likely to be bringing somethings up to consciousness for cleansing and purification. Just try not to associate the bad feeling of anger with the Mahamantra. Mahamantra is only the medicine making indigestible pains in the mind and heart come to the surface. You won't be able to progress or heal unless some things come to surface where they can be dealt with and digested as learning experience. Everyone has to come to peace within themselves and with the God first if they would experience bliss. What is bound must find release. What is grieved must find it's joy. Anger is often a reaction to something wounded, either pride or the very heart and soul of a being. In any event, our true nature is joyous praise and not these limited reactions and temporary experiences or identity. Don't stop chanting, but keep chanting. Chanting isn't the cause. Chanting is the cure.