Imac 21.5 Screen Issue

[Pajovsky]

Hi guys,

I've bought a refurbished Imac from Apple online
but had a screen issue and then they replaced it...

However the new one has a flickering issue when
it gets on the dim mode just before sleep...

Has anyone encountered this issue? is this normal?
I wanna start using my computer and don't wanna
worry again whether this imac is broken, too...

thanks for all your comments...