Murky cell shaded dark areas with artifacts on crt.

I have my crt hooked up to a htpc so this could be and likely is a videocard problem, but i want to cover all the bases.

Dark areas in games and movies almost look like extremly low quality video with a smoothing/cell shading artefact covering them.
Its like dark areas suddenly became murky gray oil spills.

Could this be a problem with my crt rear pro? or is it related to my videocard.