I am getting a humm out of home audio speakers

Now that I have connected my computer sound card directly to my home audio receiver I am getting a humm out of the home audio speakers. The RCA cable I am using is a good quality sheilded cable. When I disconnect my RCA cables comming from my DVD player on the back of my stereo receiver the noise goes away. All my audio cables are sheilded. Any idea on what could be causing this noise?

Sounds like a grounding issue. An iso transformer should solve the problem. I would suggest one on the line coming from the computer

Do You know where I could get an ISO transformer?

now that i think a little bit more about your problem you might want to isolate the DVD player with one of these boxes shown on this website

http://www.allenavionics.com/VHumElim/RCA.htm