Humming sub.

I have this sub also, slight level of hum; I was told this hum results from the servo circuit and cannot be eliminated.

You're right Eddie, there's a very very low hum left but not like it was before.

Mine has a tiny bit of hum. However, once there is a signal into it, the hum disappears. Check your cabling to the sub. It is picky about interconnects and speaker wire.

The amp may be causing the hum if too close to the sub? Isolate the amp from the sub.

Final note: Play with the volume control.

Once you lessen the hum, never mess with it again and you'll have a killer sub. I never even turn mine off.

The amp is 12 feet away.

Make sure the cables don't cross over anything else.
Try plugging the amp into a different outlet? Mine really likes a line conditioner.
Definitely try different interconnects/cables. Move the sub closer if you have to just to try different cables.
My guess is that the amp & sub hum even when the pre/pro is turned off?
Playing with that much power can cause issues...