I've recently upgraded my system from an AMD Athlon 850 MHz to an AMD Athlon 2100+. The CPU, mobo, videocard and RAM got upgraded to a higher level. The guys who did the upgrade told me that the power supply was not sufficient for the increased power consumption, so I should soon consider replacing the power supply unit. Well it works just fine, the only thing is that my sound card (SoundBlaster Live!) makes some unexplainable background noise which I can't get rid of, even if there are no events happening in the system. It's like whistling or blowing at a very low level, but loud enough to be annoying. I wonder if it is not because of the power supply unit, which, due to the increased consumption, produces some electromagnetic emission caught by the sound card. If someone has experienced the same and found a workaround, I'd appreciate your thoughts.

your sound card might be caught up with static around other expansion cards..
try to move your sound card away from other pci cards as far as possible.
or if you have on board sound, you will need to get another sound card to solve this issue.
i think there is nothing got to do with power, but what you can do just to make sure is go into bios and check voltage readings in the bios, if the power supply is overloading and its blowing hot air from the back, then you will need to get a new power supply *higher watt*
400watt is recommanded.

Agreed. The added load on your power supply can mess up the regulation of your power supply voltages. It could also emit more electrical noise(EMI). Audio circuits will be the first indication of this.

Could also be a cheap shielded cable picking up noise. This would be the one connected to the CD drive.

Some soundcards may not be "fully compatible with XP. A friend had the same experience and a new compatible card solved it.

Thank much guys!

Gonna change the power unit..