Sound card causes speakers to hum

I have the 7.1 Onkyo SRT800 speaker system and a Creative SoundBlaster Audigy SE sound card. The speakers work fine when connected to my laptop, but when connected to the sound card (in my desktop), produce a small hum. It is the same kind of hum you hear when the audio cable is live (but not plugged in anywhere) and you touch the tip, only it is a bit softer.

Drivers are installed and speakers work fine, but the hum takes away from quality...

I read up on the web and this sounds like a grounding issue, but there's gotta be a way to fix it. Any ideas?? Thanks

open the mixer panel, and disbale/mute the "line-in" and calibrate the "mic" of you have one, or mute that too.....

the hum should go away..

Ark!

Hey Ark,
Thanks for your feedback, but even muting everything didn't get rid of the hum. I just tried a couple things and it now seems like a hardware issue...

When the computer was off,
1) I unplugged the power cable to my machine. The hum continued, but when I unplugged the VGA cable, the hum stopped. The hum also stopped when the VGA cable was plugged in, but with no power to the monitor or computer.
2) This led me to believe the monitor was the problem, so I swapped the monitor, plugged it in (still with no power to computer) and the hum stopped.
3) I thought I had solved the problem, so I plugged the power cable back into the computer, and the hum came back.

Obviously, the hum seems to happen whenever there is power connected in some way through my computer. The new monitor must work differently from the old one...

I have tried removing the video card completely from the system, pulling all wires away from the sound card, disabling on-board audio, and adjusting IRQ settings in BIOS.

Is there anything else you can think of?? Thanks

Even when I plug the wire into the onboard audio port it makes the hum (not as loud though)...

The card is installed in a Shuttle XPC (model SK22G2B). The wire I have is "shielded to guard against hum" according to RadioShack.

you have multiple earth references, that is making the hum.

either:
1) your home is not grounded properly
2) the earth connection is not available to the speaker OR the monitor
3) both are earthed, BUT they are somehow mismatched.

can you run a ground wire from the mains socket to both the amp chasis and the computer chasis and the monitor chasis? if this stops the hum, tell me, and i'll give you a more permanent way to do away with the hum.

and do you have a multimeter? if you have, can you measure the voltage difference between the NEUTRAL and the EARTH pin of the Minas socket from which you are drawing the power for the computer system?