Dustin, if you mean that the hum is coming from the new sub, the first thing to check is if it's a problem in the sub amp itself. Disconnect the sub cable and turn it on with the only connection being the power cord. If there's still a hum, there's a defect in the sub amp.

If not, reconnect the cable and if you have one, plug the sub in with a "cheater" plug adapter to see if a ground loop is coming in at that point and that stops the hum. To be continued(probably).

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Enjoy the music, not the equipment.