I have a sunfire subrosa in-wall subwoofer that is making some strange noises. This is a brand new unit and it was installed correctly exactly as described in the instructions. I've attached a video where you can hear this flapping sound as the sub goes through the amplifier's EQ process. The sound is even more noticeable in movies. Does this sound like a bad unit? This is actually my SECOND unit and the first one did the same thing. Sunfire exchanged it yet I'm still having issues.