Yup. Most likely the voice coil rubbing.after trialing lots of equipment configurations, I'm 99% certain the woofer is cooked. time to replace it.
If it's a first-gen 4-Ohm version like mine, I doubt that you can order a re-cone kit for it- it was a custom build.
Contact Duke, as he's the expert.
I know that he banked a percentage of the custom order from Eminence to use as maintenance spares. If they're no longer available, he may have other options.