Computer hooked to stereo for music and have buzzing

Here's what I've got goin on. I have my computer in one room hooked up to my home theater receiver in another room by way of an RCA cable. My problem is, there is a fairly loud buzzing comming through the speakers even if the computer is turned off (but stereo still on). As soon as I unplug the computer from the electrical outlet, the buzzing goes away completely. I had this same problem in the basement of my parents house (just moved three weeks ago), and I was able to cure it by gettin an extension cord and running it from a different outlet in the basement to the power strip. No such luck here though, as I have the same problem on all the electrical outlets. Any help would be awesome as I have over 5000 songs on my computer I'd like to listen to without the buzzing. thanks.