Based On "A Childish Prank" - Na Nach Nachma
Rabbi Dovid Sears commenting on Wikipedia & Na Nach Nachma
The Na Nach "movement" was started by a group of French baalei teshuvah who discovered an elderly Breslover Chassid named Rabbi Yisrael Ber Odesser z"l in an old age home in Eretz Yisrael. When they heard his story about having received a "petek" or letter from Rebbe Nachman when he was a bochur in Slonimer Yeshivah, they believed Reb Yisrael Ber and began to disseminate the now-famous petek and the "mantra" it contained: "Na Nach Nachma Nachman me-Uman!"
This is evidently based upon the Shem be-Achorayim, which the Rebbe mentions in Likkutei Moharan II, 8 (the last lesson the Rebbe gave, also known as "Tiku / Tochakhah"). Whoever invented the petek substituted the Rebbe's name for the Shem HaVaYaH and added "me-Uman."
I was personally told by Rav Zvi Ashkenazi, a Slonimer Chassid and one of the leading shochtim u'bodkim in America, that his grandfather had written the petek and tucked it into one of Reb Yisrael Ber's seforim as a childish prank. But when he told his extremely devout and temimusdikeh classmate that it was a joke, Reb Yisrael Ber refused to believe him. (Which shows you the danger of letzonus!)
The Na Nach group is a totally marginal phenomenon in Breslov today and not one Breslover gadol buys the business of the petek. But for these kids, the Na Nach sect with its rejection of middle class culture and its pursuit of electric niggunim ecstacy is a way to express themselves in a religious world that for one reason or another they can't relate to.
Being strongly committed to the Breslov mesorah, I can't endorse the Na Nach thing; but I also can't negate a movement that keeps many kids basically within the geder of Yiddishkeit, and which doesn't seem to be doing any major harm that I know about. Reb Yisrael Ber also left a small fortune of money that people gave him to publish the Breslover seforim, and his group has probably done more to publish and disseminate these books than anyone in Breslov history. If the Na Nachs would turn down their amplifiers in Uman I might be even more liberal-minded about them -- but as the saying goes, "that will be the day!"