I just recently purchased

Cambridge SoundWorks
FPS1800

and I'm hearing this
DUB, DUB, DUB... DUB DUB DUB DUB....
... deep bass sound from my woofer..

First I thought it was my SBlive's distortion... But even when I unplugged all except power and control lines, the sub still made this
DUB-DUB-DUB
deep sounds, which is CLEARLY noticeable..

From your experience, is this kind of deep low -dub-dub-dub sound normal for subwoofers?
Or just this certain woofer?
Coz my 14 day money back guarantee is running quick.

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The world is doomed