USB to audio adapter or other fix...

Hi here's my problem - Sometimes i hook up my macbook pro to my LCD tv to watch movies and the video is fine but when i hook up my audio cable there is a lot of high pitched screechy noise that comes from my tv's speakers. I don't think the problem is the cable because there is no noise until it is plugged into the computer. I'm looking for a cheap usb to audio adapter or if someone knows how to fix this otherwise, let me know. I looked on ebay and there are some cheap ones but none state that they will work for mac. Also i think the Griffin imic is too expensive for what i need it for. Any alternatives? Thanks!

do you have an xbox 360? if you do look into connect 360. that works for me. i'm not real sure about that usb deal.