What will happen if i take my hacked phone to repair it?

i have an epic 4g from sprint and i have a warranty for it. i put a new rom in the phone because i didn't like stock rom. Recently my speakers arent working and the phone is now really slow and its not because of the app because it was working fine until recently. my question is if i take it to the sprint"headquarters" will they take it or theyll just fix it or give me a new one?