I have the sound group II and today when I put up the volume to about 20 I heard this awful rattle coming from the back of the car. It sounded like I blew a speaker. I got out of the car and went to the back to hear the sound and I leaned on the rear decklid and the noise stopped. Now I don't know what to do. Does anyone else hear the same thing when the volume is at 20 or above when your listening to a song with a little bit of bass?