subwoofer problems

[mr karnage]

my subwoofer has started making a clapping sound whenever i play certain tracks, it doesnt happen with all of them. at low volumes its fine but when i put it up a few notches and it starts making a clapping sound even though its hardly moving. when i first bought it i played it at nearly full volume and the shit was shaking up my whole house, my neighbors told me they couldnt hear their tv and you could see the sub moving. it has just started now but what could it be, is the sub on its way out?

 

[mr karnage]

dont matter ive sorted it, it was because i bridged the sub and didnt set the gain.