Hum on Auxiliary input of Dell Inspiron 580

I want to record audio on the auxiliary input of my Dell Inspiron 580 but there is hum in the line and I'm wondering if there's a ground missing inside the computer or that a filter capacitor is bad in the computer. Connecting a USB interface also has hum and it is too much hum to record audio. The auxiliary input is able to receive an audio signal but is sending significant hum to the output of my monitoring amplifier. My father had the computer serviced once but not for this problem and I don't know what problem he had because he passed away. It is a Windows 7 computer with Linux installed and working properly. The auxiliary input is sending hum to the monitoring amplifier. You would normally think that hum would come from an output. Do I have to open the desktop and check somewhere? I never opened a computer before.