Panasonic Plasma Problem

[gordon lonsdale]

Every time I switch on my 3 month old panasonic plasma the picture picture breaks down (depixellates?)in sections of the sceen and is accompanied by a matching breakdown in the sound . After maybe 15-20 minutes it stabilises and is no problem , it never happens when playing dvd's and is never quite as bad in analogue mode. Anybody experienced similar ? Any explanations