there seems to be these flapping sound coming from the sides of the rear when bass is up. anyone knows what this could be?

 

From inside? - The child safety seat latches on the rear deck.

 

Any subs in the trunk?

 

i have the mtx box in the trunk. the flapping sound some from the outside like where the back side markers are. its annoying. i've checked underneath but nothing. do the side markers just pull out?

 

Be glad that noise is there. Behind the marker lights, there's a hole in your quarterpanel, with a plastic frame and a few rubber flaps. These are vents that are necessary to allow you to open and close your doors. When you slam your door shut, the air in the cabin escapes out of those flaps. Without them, your doors would be hard to close, and if you defeated the flaps, you could end up damaging the seals and weatherstrips on your car. Then, think windnoise and water leaks. Just something to live with man. Besides, you can't hear it when you're inside, and you didn't blow that kind of money on your stereo so that the people in the car next to you can enjoy it. And if you did, they're probably annoyed with the level of sound - the flap isn't going to bother them.
Hope that answers your question.

 

thanks, i think that could be the problem. yeah cant really hear it inside but its annoying when outside the car and could hear something flapping around in the back. i already have dynamat, will try adding more or something to keep it down. if not, i guess i will continue to live with it. thanks man