I've been playing a lot of the Wii recently, and I've noticed some strange behaviour from the TV, which is a Sony Bravia. Every time I turn on the TV and start using the Wii (in AV input #3: component), after a while, somewhere vaguely between 5 minutes and half an hour, the TV spontaneously switches to the Virgin Box (which is on AV input #1: SCART, and on standby). As far as I can tell, it doesn't happen again so long as the power remains on. So who's the culprit? The suspects:
The TV remote
I think it's unlikely. It happens enough that I'm pretty sure that the remote hasn't always been in a position to do it. Also, the fact that it never seems to happen twice in the one power-cycle seems to count against this possibility.
The Wii -OR- the component cable
I suppose this could be possible: perhaps an interruption of the TV signal would make the TV think it's been disconnected and change the channel. I'm still not sure why it would only happen once per power-cycle.
The Virgin box
Another possibility: I think SCART devices can signal to the TV that they have turned on and it should switch to them. Perhaps something's causing it to send this signal occasionally?
This might be most likely. It would be the only thing that really explains why it happens once per power-cycle, although even then I have no idea of the mechanism. It would be a right pain, since it's the most expensive of all the things that might be broken!