For some reason,
I thought it would be a good idea to see if the scraping was
on the in stroke or the out stroke of the woofer piston.
Being the genius that I am, I loaded up Audio Test Bench and
proceeded to send 20 Hz to the woofers.
"Boy, isn't this fun, let's do 10 Hz."
"Hey 5 Hz looks cool, I can almost tell when they're scraping."
"Hmmm, nothing at 1 Hz, let's try 1.5 Hz. Cool, it scrapes on the way out."
"Hey, what's that smell? Oh shit! varnish! fuckfuckfuck!"
running for the power switch.....
So now it's time to let things cool off and perhaps take up nail biting again...
And perhaps switch to a smaller fuse.
EDIT: Turns out the smell is coming from the other channel,
which, thankfully, seems to be firing on all 4 cylinders.