Vandersteen problem

Is the woofer vibrating against the cabinet? It may be as simple as needing to be tightened and secured.

It's a major pain getting at the drivers in a Vandy, given the way that the sock is stretched and attached over the frame. If repair is needed and you want the speaker to look good again, then you will almost certainly need a competent dealer's help, or send it back to Vandersteen.

The noise you describe suggests the possibility of a blown woofer. Hope it turns out to be something less...

Its probably the Rim seal on the front 8 inch woofer
if you don't have a local Vandersteen dealer to bring
it to you can
remove bases flip it upside down remove the screws and
lower wood panel slowly from the back with a flat wide blade
screwdriver now pull out all staples and pull down the
fabric inspect the 8 inch and you may see the problem.
remove driver and call vandersteen for repair reinstall driver and staple back the grill evenly and you are finished .
John

Here's a pdf of how to get the speaker apart:

http://www.vandersteen.com/pages/Pdffiles/RepairIns.pdf