I have a problem in Mental Ray.

The problem is this: sometimes a character's brightness suddenly pop ups and/or pops down. So that that character can seem to be flickering. For example, my character is rising on it's hind legs and right before it reaches its apex. The entire character gets brighter in a jump that seems to occur in one frame.

The character is on its own render layer and all the other elements the primary visiability is turned off. In the process of trying to figure what is going on, I've have layer override the raytracing to off and it still does it. I also rendered in Maya software and there is no popping of the brightness.

I think I can fix it in post using photoshop or after effects. But has this happen to anyone else? This is my frist time in rendering out a animation with mental ray