I just got my new CX-7 and noticed that the rear subs(speakers) in the back two doors have no bass at all. Is this the norm in CX-7s or should I take it back to Mazda to have them look at it? The front two speakers in the door and in the dash sound great, however move the sound to the back, and it reminds me of Sparkomatic speakers, pure treble. Please tell me this is not the norm.