Clicking noise with M-Audio Audiophile USB

I just got an M-Audio Audiophile USB, and the quality of the music from my pc is definitely better than the internal card. However, no i have a worse problem than before. When i play music on my computer through my home stereo there is a significant clicking noise that comes out of my speakers about every five seconds. It's hard to decribe the exact sound in words, sort of a noisy distorted click about every five seconds. I know the problem lies with the M-Audio card cause my speakers sound perfect when i'm not playing music through the computer. Is this problem due to the fact that the card is externally connected to the computer with a usb cable. Before I got this product i was wondering whether a usb hookup is a good thing. I wonder if my suspicions were correct. The cable length is about 10-12 feet, so it's not extremely long. I also noticed, that when my CPU is working really hard, the music I'm playing on my computer sounds horrible, full of distortion and completely unlistenable. But even when all i'm doing is playing music through winamp, i get that terrible click every 5 seconds or so. What's my problem here?