Have anyone installed a new head unit in 2006-2007 Sonata. If yes, is the harness the only thing we need or there are some tricks with the factory amp we have to do? I put in a new unit yesterday using a harness I got from Scosche ( HY05B ) and everything works but the sound comes out too low. When I turn the volume half way its still very low, but starts to get distorted like when you crank it too loud only its not loud. Any ideas? I think I used a wrong harness or maybe not, I ordered a new one from Crutchfield just in case.