Is the woofer vibrating against the cabinet? It may be as simple as needing to be tightened and secured.
Vandersteen problem
I am currently trying out a pair of 2CE speakers and notice distortion in 1 speaker with fairly low frequency present. If I lightly place my outstretched had against the rim of the woofer the distortion goes away. Is this a sign of a bad woofer or could it be something much simpler and less costly? I would imagine due to the nature of their construction I'll have to cart them off to a dealer?