Rendering wireframe

Hi guys,

I have a bit of a problem I would like you to help me solve.

Recently I was rendering model images in wireframe and ocassionaly I happen to see "ink spots" on the white space where they shoulnd't be.

You can see some black spots/lines on the heatsink. The bigger assembly the more of this appears. These are obviously some part lines that should stay behing and should be invisible but for some reasons it all comes out.

Is there anything I can do to get rig of these lines/spots?

Kind regards,

Michal

SolidworksPhotoview 360