Hi Guys,
I'd just like to suggest a few issues/cures
The clicking, buzzing or ticking noises are likely to be results of emissions of other components in the PC. The speakers attached to your sound card are most likely to be attached to an analogue output and as such the signal from them is directly influenced by what the sound card is outputting.
You may have the gain (or volume, if you will) turned up too high on either your sound card or your speakers, so they're emitting more noise than they would at ideal levels. More expensive speakers have better shielding. You get what you pay for, I'm afraid.
You could also be getting interference if your PC is running on the same mains feed as your speakers. You can buy mains adaptors that 'clean up' your electricity feed. People who are keen on their hi-fis buy these sometimes.
Solutions:
1)Use a digital feed from your sound card / onboard sound card. Make sure it's set to output only digital signals, not a combination of digital and analogue. Using an A/V receiver, such as a dolby digital decoder that might come with a surround sound kit, you'll only be decoding what is pure audio. You may still get interference if your speakers are not connected to the A/V receiver with decent cabling.
2) Your problems could simply be because the sound card is inside your PC, which plugs into your mouse and keyboard (of course). Devices still use IRQs and so everything goes through the processor, so signals can still get mixed, so to speak. Overclocking and upping voltages can't help. Try buying a new soundcard which has an external breakout box, could help.