Humming sub.

I tried to teach it the words to no avail.
Velodyne ULD 15, low hum when powered up, can't hear it when music is playing. It does not vary with volume on the servo controller amp.
Any guesses what it might be? I tried different cables and checked connections.
Sounds like ground loop hum, if it is, cheater plugging the entire system is the only way I've ever been able to get rid of it.

FYI, I've run in his configuration for quite some time without any problems. And with absolute silence.
get a Cheater Plug (unground the sub), if it goes away you have a ground loop problem.
Unplug your Coax from your cable box and see if the hum goes away.
Ok thanks, I'll try that.
Sometimes if your sub is on the same curcuit as the lights (especially with dimmers or 2 or 3 way switches) it can cause a hum. Turn off the lights and see what happens.
Do a web search on ground loops. There's quite a bit of helpful information. There are safety concerns with running a component with its ground defeated. Look into line level isolation transformers to break the ground as a safe solution.
I have this sub also, slight level of hum; I was told this hum results from the servo circuit and cannot be eliminated.
It's not the lights, floating ground solved it. I'll check the web for ground loop info and see if there's a better solution.

Thanks all.
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...
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.
One of the best places to search for this hum is in the video section of your system (TV, DVD, VCR, etc). While the sub is on with no music just hum unscrew your cable TV from the wall and see if that does not get rid of your hum. I had the same problem and that was it. I just happen to have a ground breaker for my cable and now it is gone. Another thing that works great is one of those filters that you buy for your car system to keep the alternator noise out. Put that on the problem and that will work. Of course, you will loose some of your sound quality with the cheap interconnect wires on it but you will have NO noise. Hope this helps and if someone else said these things already forgive me.