Grey spots on screen of new Ipod

I purchased a new ipod Gen 4 on the internet, 4 weeks later I have 4 grey blotches on the screen, Ipod was sealed when i purchased it, It was not been dropped, The first grey blotch showed up within 2 weeks and i now have 4 blotches on screen . Before I contact paypal I need to know whats going on

Thanks