anyway its magnetic interfearence causing the problem. i used to get it with my cheap 19" monitor as it had no shielding. now the cheap 19" is the slave monitor on the table next to me well out the way of the telly, i now have a 19" pro hansol monitor and it has a magnectic shield all the way round the inside of the case and does not allow the TV to interfere with it.
Yes it is your monitor causing the problem. I have 2 monitors side by side and one of them doesn't have good shielding, they both have 1 line taking about 26 seconds to travel, one going up on one monitor and one going down on the other monitor. It's only one line since they are both at ~60hz (ouch)
granted, but i think you will find the offending monitor and telly have no form of magnetic shielding, can be confirmed by holding a magnet to the side of the telly/monitor (this is not a wise thing to do kids, might fubar the pic forever)
Most of the interference comes from the monitor but any part of the PC can cause interference. There should be little FCC (USA) and EC (Europe) stickers every part in your PC. The stickers signify electromagnetic interference (EMI) compliance and there are different grade (home, commercial, industrial, medical, etc.) Some manufacturers (cheap generics) may not have tested and certified their equipment for low interference. Or they may be certified for industrial where things like TV's not have static are not important but then sold for home use.
My last monitor that had to be switched off if I was going to watch TV on channels 4 or 5. The new one I can't even tell if it's on. My TV is about 20 feet from the computer with 3 walls in between!
Cheap power supplies cna be another nasty source of TV interference. I also had problems with an old mother board back in my 550 mHz K6-2 days.
Not much you can do to fix it either. Once the EMI gets out of the box there's nothing much you can do to contain it. It will couple inot power lines, antennas speaker wires etc.