Try a different power supply.

What he said

Sounds more like just a bad set of speakers Jim, are they under warranty?

That'll be the reason...

If a microphone is connected, disconnect it.

The "noise" could be from a dimmer, also. You might try shielding the wiring to the speakers as well.

If all else fails, try:

Moving to another state.

Getting a house with no fluorescent lights.

Getting a pair of logitech speakers.

And no moonshine.

Tinnitus

[Creative 5.1 surround speaker set.] not enough info- what is the model ?

I guess these have an active subwoofer ?
Are the speakers all connected to another and end in one powercord that is also attached to the active sub? (soundsystems)   that have just one main control unit often do.
Or do the Satelites that have seperate cables for each one aswell as the sub? 

Try and check if the cable of the sub is loose / these tend to be cheap and have no permanent lock could got wobbly also while on it turn the bass down to 50% if the sound still persists and the satelites have extra cables unplug them from the main volume control unit one by one *if the active sub is seperatly powered disconnect it while doing so to see if the cable of the sub is faulty.

Another idea: Have you replaced the standart cables that came with the product?
The idea is that if you did and replaced them with something longer  the problem could be on the new cable- apparently the signal is tuned to the given cable lenght on some systems therefore a replacement has to be from the manufacturer and cant be replaced with just *any cable.

Unless it began exactly with the new speakers, it could be nearly anything else nearby throwing off EM noise and the speaker wires are just picking it up like an antenna. Some newer video cards are notorious for doing that.

You could try getting a surge protector that cleans the power. I'm guessing the cables for that creative system aren't all that great? Even if they are sometimes, it doesn't matter.

Try something like this: http://www.sweetwater.com/store/detail/PRO800/

I have the rackmount version, and it works great. They can be expensive, but if you want the noise removed (if the noise is from dirty power), they work well.

Yes.

creative inspire t6160 5.1 surround

Bought at pawn shop. Look like new condition.

Began with the new speakers, Logitechs don't do it, but they're just two speakers and a sub.

just took a look at it all the sat´s end up beeing plugged into the active sub and the sub has a control unit...
however a single cable for the subwoofer and the center is used...

I would say it is the subwoofer
Turn the bass level/volume down *on the subwoofers back and test if the *noise is reduced, if not working then unplug the center reduce the bass volume again and listen to a rear speaker satelite if the sound is still there .

Well, it seems that moving the sub farther away from the PC fixed it. Apparently it was too close to all the wiring coming out of the back of my PC.

Thanks for all the help, guys!

Yall rock!