its time for a new one... its looking like its the voice coil....

Do you get any sound out of the old sub, like crackling or anything? Did you also check the tinsel lead on the back of the sub that goes to the cone?

Also, before you replace the sub, I would also check your gain setting. If its too high, your amp will send a clipped signal to the sub and you will end up in the same situation as you are now.

The Gain is the input sensitivity that tells the amp how fast to go to full power based on the voltage output of the head unit {Volume}.

For example, if your preout voltage is 5 volts and your amp gain is all the way up, then when you turn your volume **** to 1/4 or more, your amp is putting out full power, then you crank on it a lil more and before you know it your clipping the amp and destroying your speaker.

Basically, your amp should put out full power when your volume **** is about all the way up.

The best way to set the gain is to turn the gain all the way down, and turn your head units volume up to about 3/4 the way up, then go to the gain and turn it up until you hear your sub distort, then back it down until the distortion is gone. You have just propely set your amps gain.

P.*. this is assuming that your amps Ohm load and power output matches your subs Ohm configuration and power rating.

I had an enclosure once with a bad terminal box in it. Anytime leads were hooked up on it, and any volume was sent through it, it would send the amp into protection mode.

Had to cut a rectangle for a new connection, and put a new terminal in.