I have a HK sub and its about 6 months old. i have loved the bass it gives or gave. i am now hearing a flapping noise from where the wind comes out from the back, i am sure its coming out from there. i only hear it when i have the volume at about +65. the thing is this never happened b4 and i will be honest i listen to alot of music and crank it loud. i took a look at the sub while it was on and it seemed fine. the cone works fine. is there something i can do, like play around with the back of the sub, it has alot of dials which i have never touched. now keep in mind when this noise comes i can still hear/feel the bass also.