I've got a hum in my Sunfire sub.....

I had a boston acoustics sub once that would hum if I bumped the RCA cable end hooked into the sub itself. Bumping it again or shaking it would make it good with the world again. I wish I had a more scientific reply, but you never know.

Bad solder joint on ground on front RCA jack?

Try floating the ground pin of the powercord.

try buying a grounding plug on the end that converts the 3 pin from the sub to a 2 pin for your wall. Often the ground pin causes the buzz.

JWH