C1 4 adds a lot of sharpening by default, have you tried reducing this or turning it off?
Obviously sharpening enhances noise, so if you are going to do some NR work on images, I would avoid any sharpening, or keep it to a minimal level.
I have noticed, that even with sharpening off, C1 does seem to apply some anyway, this is one of the weak spots of the software IMO, but it's still very good, and right up there for details work.