Handsfree is working bad

I have a BLU Studio 5.0 S II only with 3 days of use. When i connect the handsfree, the sound seems like if have an effect, like ECO, and the music hear bad. But i press the handsfree´s bottom and everything is perfect, the sound is good. Is a problem of my cel or is and adjustment that i have to do? I look in all settings and nothing. Please help me.