The ATF won't do much. When you change oil, use one of the universal grades like Delo 400, Rotella T or Mobil Delvac. The added detergents in these oils will go a long way toward cleaning it out. Drain the oil when the engine is hot and preferably overnight. Change the universal grade and its filter about every 500 miles, draining it hot and overnight until the noise is gone.

Good luck,