I have a 2011 4.6 and I noticed that the sound isn't as balanced. I sat in the back seat and played around with the fader settings. Once with the sound in the middle and I heard the front speakers more than one full sound. Then I panned the sound to just the rear speakers and the rear speakers were very very low. The volume was on about 19 or 20. Is this normal or are my rear speakers going bad?