Upgrading the power cord can make a big difference, especially if you live in an area with lots of RFI, or in an apartment or older building. I live near the Dulles airport, and it made a big difference in video and sound when I upgraded my DVD player cord. If you want to try a cheap alternative first, try a $25 power wrap from amusicdirect.com. just wrap it around your standard power cord and give it a chance. You can also put it on your receiver, tv, cable/satellite box. If you see a difference you may want to upgrade those components with real power cords. You don't have to spend a lot of upgraded cords, either.
http://www.amusicdirect.com/products/detail.asp?cat=280&sku=AHW02
http://www.amusicdirect.com/products/detail.asp?cat=280&sku=AHW02