I sent this trick to a friend who had a humming Sunfire sub that many said needed to be internally rewired.
Here is what did the trick.
Take a thin run of plastic coated wire from Radio shack, find a screw on the metal plate of the sub and attach one end of the wire.Now take the other end of the wire and see where in your system the hum stops as you touch the chassis of your components.When this didn't work I told him to touch the screw on the plastic plate cover where his sub was powere at the wall outlet. I did this to get hum out of a Phono stage.Bingo, no hum from the sub.
Here is what did the trick.
Take a thin run of plastic coated wire from Radio shack, find a screw on the metal plate of the sub and attach one end of the wire.Now take the other end of the wire and see where in your system the hum stops as you touch the chassis of your components.When this didn't work I told him to touch the screw on the plastic plate cover where his sub was powere at the wall outlet. I did this to get hum out of a Phono stage.Bingo, no hum from the sub.