Hoenn Sound is a feature in HeartGold and SoulSilver, active every Wednesday when the player tunes into their radio's music channel. Hoenn Sound attracts Pokémon native to the Hoenn region.
Finding and catching Pokémon exclusive to the Hoenn sound feature is done in a similar manner to catching Pokémon native to the region the player is catching it in. The radio must be playing while in tall grass, meaning that every time the player does battle, or switches to a new area, they must turn on your radio again. This is most definitely hindrance when catching rare Pokémon with the Hoenn sound.