Why have you got a loud hum on your audio playback?

This is usually an electrical short or electrical interference somewhere in the audio pipeline. First, try using a different audio jack, if you have more than one choice (most computers have one on back and one on front, sometimes more). If that does not clear up the hum, try using a different set of speakers or headphones. If that does not work, look at nearby appliances, such as cable boxes, cordless phones, etc, and see if unplugging/turning off these devices corrects the problem. All devices should be FCC Part 15 compliant, but sometimes they are not if the shielding breaks after inspection. Other less common problems can include faulty sound card, motherboard, audio converter, or power supply, but these should be checked only after exhausting all less troublesome options.