Thanks a lot for your reply Hybrys. I'm trying to understand your suggestion... Are you saying I take a wire that's connected to a ground, and touch it to the computer case?

I'm so happy to have found this thread after weeks and weeks of searching about this problem. The noise has been driving me nuts, and it's only after buying and installing a sound card with front panel pins that I've realized the problem is with my headphone connector, not my motherboard audio...