Trying to fix sub woofer humming noise.

Hello,

I recently moved back into a college apartment. When I plugged in my Altec Lansing VS4121BLK speakers to listen to some music. I noticed a low humming or buzzing noise coming from the sub woofer. I went online and started trouble shooting I read a few articles about something called ground loop issues. However, I'm not sure if this is the issue with my speaker system. I tried plugging it into various different outlets and power strips and it still makes the noise. so I started to unplug wires from the back of the sub woofer one at a time.

Bear in mind that this sub woofer connects directly to the wall from itself to get power using a two prong outlet. The rest of the audio system connects to the back of the sub woofer. It has two speakers each one has its own wire that connects to the sub woofer. the right speaker has the power button for the system, volume control knob, treble, and bass control knobs. When you turn the bass knob to far left or right the hum is very noticeable and if you leave it in the center it is close to unnoticeable.

Back to talking about removing the cables one by one. When I leave the system plugged in and remove the right speaker connector from the back of the sub woofer the humming noise goes away completely. I don't know what this means but there is power going to the system and I think this eliminates the possibility of a ground loop issues since all I did was remove the right speaker connection. What could this be an issue of and how can I solve this humming noise with my sub woofer?

Thank you,
Fruhstuck