I really did spend a lot of time trying to track that one down. Checked wiring in walls and ceiling, objects in the adjacent room... nothing made sense. No other structures nearby either. The house's electrical panel isn't too far away, but it's the exact same distance from what ended up being an okay position.

In a completely different part of the basement about 30 feet away, service guys went through 3 Philips 34" CRT televisions trying to get one where the red didn't shift severely along the edges to magenta. Never did get it perfect, but the problem was extremely rotation sensitive - they had to play around with adding magnets while in was in place.

I dunno. Some kind of meteorite buried in the front yard? :-)