What's that buzz, tell me what's a happening...

Playing Radio Head's "Pyramid Song" (a little loud but not even 10 watts) where Thom Yorke's eerie hum begins and one of my speakers starts to make a vibrating sound like a cheap old phonograph! I figure its inside the box, maybe behind the woofer. Almost sounds like a screw is loose and matching frequencies are causing it to vibrate and sing. This has never happened before!

"S**t" says I, and I start putting pressure on every screw head, binding post, sides of the cabinet etc to no avail. "S**t" says I again. I want to rip apart the woofer, get in there and hot glue everything. Probably not a good idea.

Ya think I can take the screws off the woofer or the binding post plastic housing thingee (or both) to take a peek? Is this a typical DIY thing to do? We're talking Totem Sttafs. What do you think could be loose in there? Or is it something more ominous...:-(