Horrible pixels when fade out

Hi guys,
I've been working on a comercial and in the final render I can see that pixel thing when I fade out.
That must be about the render settings, but I don't know why it happens.

My settings:

I've been working on a comercial and in the final render I can see that pixel thing when I fade out.
That must be about the render settings, but I don't know why it happens.

My settings:
