Hello. I purchased Prius v Three about a month ago. When I was playing music, I noticed that I wasn't hearing sound from the rear speakers even when I sit in the rear seat. I tried making the sound come out only from the rear speakers and they're working, but it's so much weaker than the front speakers. I need to make it 80%-90% from rear to balance front/rear sound. Is this normal or does my Prius have problem?