This television displays a strange image and sound distortion just after
it's been turned on, as shown in this 5 second video.

http://www.youtube.com/watch?v=usQFxTJ04s4

It may do this several times, and, rather disconcertingly, seems to be
slowly getting worse.

Note - the slight flickering is an artefact of the video recording.

I'm using a computer output to show the fault, but I get the same
behaviour on broadcast channels if the computer is completely
disconnected, and turned off.

I suspect a warming up effect. Any ideas?

Sylvia.