hi steve, never heard of the term dirty screen before, but it could be something to do with 'burn in' which plasma screens can suffer with, it means any permanant image on the screen if viewed for long periods can ghost onto the screen even when you change the channel, like the sky sports logos, ceebeebies and the like, alot of new screens recognise this and move the image around the screen but only by very small amounts so you dont visably notice it. the bit about changing some settings also sound like garbage, some people cant help themselves and start adjusting settings thinking it is for the good, my opinion is when you spend over a grand for a tv it shouldn't need adjusting, and if it does send the thing back, i have a samsung 32 and i havntaltered a thing on it and its still perfect 6months later