How Do I eliminate Humming and Buzzing from my computer speaker system?

Could be your receiver. Have you tried a different input? I bet it's just your computer making the frequency and it's being conducted through those cables. If they're cheapies, they might not have any sort of shielding. Try Monster Cable 3.5mm jack to stereo (rca) cable. 8' long and works great! If that fails, a shot in the dark might be moving your cell phone out of the room. GSM phones (Tmobile/ ATT) have been know to interfere with speakers at short distances. Good luck

TURN IT DOWN!!!!!!!!!!

It could be a couple of things that could be causing this issue. First the most common is a ground loop. This is when two or more components are sharing a common ground and are out of phase. If you have two components or speaker that are on two separate AC outlets and each outlet is from separate sides of the electrical panel they are out of phase and you will get a ground loop. A few ways to fix this is make sure they are plugged into the same outlet ( as long as they are not two high current sources, amplifiers for example). Or you can use a ground lifter which you can get at any hardware store, its 3 prong to 2 prong AC adapter or its called a ground lifter. Un-ground the computer speakers and that may resolve the ground loop. Dimmer switches on the same outlet will cause humming or buzzing noises in the system as will refrigerators. Make sure no interconnects are running parallel (along side of ) power cords, this can cause humming through the system. A default in the output capacitors of the receiver can cause this sound which a defect and needs repair. Output capacitors go bad over time so if its a older reciever that is a common issue. That is most of the issues that can cause this and check each one and you should find the issue. Kevin 40 years high end audio video specialist