I’ve had a similar problem like that! My TV will pop up a black rectangle that takes up about half the screen and it will start displaying a bunch of jibberish, or actually sometimes stuff that looks like URLs. The only way to get rid of it is to change the channel. Also, it only happens on some channels. I’ve never been able to figure out what it’s from. The TV is about 7 years old and this only started happening recently. This, of course, is no help to you, but I didn’t know anyone else had the same problem :P