Thanks for all the replies! It seems as though Quall999 has solved the great mystery! When the line first appeared, we had just gotten a new receiver and a new digital cable box. Being certain after reading these replies that it was one them, we unplugged them but the line was still there.
Then two nights ago when Hurricane Jeanne was rolling into town, we had to unplug all of our electronic components. When we just plugged the xbox back in.. the line wasn't there. One by one we tried plugging in devices.. no line! Then Tivo
Seems as though Tivo is the culprit!
Tonight I'm going to try to re-route the Tivo power to the back of the house to see if it might cure the line. Weird thing is that the line isn't there for any of the other devices.. just the xbox when Tivo is on. Very odd!
Thanks again for your help!
panch