when i crank up the bass in the car.. my sub seems to be making funny rattling noises. It seems it is coming from where the cone is... as if when it comes out and hitting something on the way back in... anyone know what is the cause of this?

 

You could be over powering your subs....that sound could be the subwoofer voice coil and cone actually bottoming out!!!! It would sound like a pop.

 

the sub is 150rms and my amp is 150 bridged... sub can take 400 peak... i have gain about 65%.... does it mean the subs just suck?
what can i do to stop this from happening?

it sound like a buzzing/rattling sound during long bass... mainly coming from cone area..

 

Try turning the gain down a little bit....if you are running the stock head unit...it could be distortion.