Hello Cristen,
Hum is caused in most cases by a "floating" earth in the audio gear.
There are several methods to try and make the noise go
away.
First off, are you running a normal 600ohm insert, if so, are the wires connecting it connected in the correct manner, check them if you can.
If any of the wires inside the cord are open circuit, you could get a similar effect.
Try cleaning the plugs on all the leads, mabe there is a bad connection in a socket.
Some audio equipment provide a "Earth" link, usually a single black wire that one can "earth" their record player to the amplifier.
If you have this facility, and if the hum is there when this "earth" wire is connected, try disconnecting it and see if the hum dissapears.
Some times a switch is provided, sheck if you have one, usually on hi end gear.
The equipment might have an internal fault in the power supply, leaky capacitor, power diode open circuit or breaking down under load, then take it to a electronics repairman, don't fix it yourself unless you are qualified to do so.
Good luck