V-1B M&K Subwoofer has a load humm

Question

As you can imagine, I've had these speakers for over 30 years. The woofer is now making a humm and the only thing I can do is unplug it (the satellites are working fine). I don't know where to go to get it repaired, or if I can do it myself...I'm not a wirehead.
Thanks,
Mike