I cant be 100% positive without seeing the problem myself or having more info about it but it sounds like it could be 2 things.
1. The sound card is defective or the contacts may need to be cleaned both inside the computer and the back of the card.
2. It could be a cheap intigrated motherboard sound card with creative drivers that makes it "look" like its a creative card when its actually not. With built-in motherboard sound cards, whirring noises and hissing is common and there isnt much to do other than upgrading the card.
More information could be useful, what is the make of the PC, is it custom made, have you upgraded the sound card, when did the problem start, was it doing it before????
John