Humming comes in audio systems because of 1) improper earthing 2) bad circuit. In case of (2), you have no choice but to go and get a better system or plugin some higher capacity capacitors in your circuit. (1) was my problem and I got this really awesome solution to it. Its called the perfect JUGAAD (
click here for wiki's definition :D).
The place I put up in has no earthing. Whenever I connect my laptop, I feel minor shocks at times and there's a lot of humming in the speakers when I connect the audio cable to it. I confirmed the earthing problem by running the laptop on batteries. When I did that, I got no humming sound when there was no audio playing.
Today, I thought of connecting the analog cable to my lappy and check out its TV tuner card. Amazingly, I got no humming disturbance when I connected the cable TV wire! That means all the extra current was flowing out from the cable down into the earth. :D Talk about getting cheap and perfect solutions ;)