60 Hz Hum from Powered Sub

If you're going to open it, be careful to discharge all large electrolytic capacitors through a resistor. These caps can store some high and potentially lethal voltages for a long time. All plate amps I've worked on use 105C capacitors.

I assume the DC power supply uses full wave rectification.

: a rectifier that converts alternating current into continuous current and that utilizes both halves of each cycle of the alternating current.

120 ripples per second.
I would think if it is a bad electrolytic cap in the DC power supply the hum buzz would sound like this:

120Hz Hum
https://www.youtube.com/watch?v=pC4Uzt0qm2E

or this,

Like a 120Hz buzz
https://www.youtube.com/watch?v=pf-vULfjYK8

If you added a new electrical device, it could be anything from a cooktop to a heater. This device could be causing a DC on mains issue which causes  the transformer to buzz. So you need to isolate the noise. If the driver is making the noise, it is most likely a ground issue somewhere, aging components or aging sub cable with deteriorating connector. If the transformer is buzzing, it is most likely the DC on mains issue. Emotiva makes a specialty filter that works if that is the issue. If the sub is old, its not worth fixing unless it has a special connection for some reason.  

Spacecadet3;
moving it around to rule out ground loops is nonsensical.  ground loops will occur whenever there are two different paths to ground. By moving it you guaranty a different path!

Every single solitary component in your sonic chain must b grounded to the same circuit, preferably to the same outlet.  The best way i know to achieve this is to have a 20A outlet, and buy the biggest, heaviest duty outlet strip you can get and plug everything into that.
if you need to daisy-=chain them do so. But use heavy strips with heavy cables and preferably upgraded or even hospital plugs.  Why? solid, high current contacts.  the $15 is well spent.

However, you said it "developed" a hum. You didn't say "i rearranged stuff and suddenly there was a hum". Be clear which was it?  if it just developed with no changes then indeed you likely have a problem in the woofer and it requires service. A loose ground, bad connection, or failing capacity or among myriad other reasons....

I doubt its a big deal, but qualified labor is not cheap.

Good luck, noise issues can be buggers.
G

It definitely "developed" the hum. It has been in the same location for about 6 months and it's just begun making the noice in the past 2-3 weeks. From all of the comments collectively, it would appear that the amp has caps that are failing. I'm not sure I have the time or interest to mess with it. It will probably be retired.

Thanks to all of you for the great responses!

G