kicker l7 flapping noise?
 

Hi guys I bought a second hand kicker l7 it absolutely cranks but I noticed when the bass goes real low it makes a strange flapping or vibrating noise. It does it even at relatively low volume and only when the sound is a deeper lower frequency, any one have any ideas what it might be? I understand it could just be blown but I don't think so because if still cranks like all hell.