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.
homer
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.
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.
Post removed 
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.