No ground screw on that old sub.

If you have cable connected up to the receiver, try disconnecting it.

BTW, not sure you are aware but you can trade that old sub in for a new one. I'd bet even the least expensive Axiom sub (EP125) is better than that one. I have two EP125s and like them very much. I also have four EP500s, two EP600s and an 800. I really like them all! smile

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated