I'm seeing the 'noise' predominantly in the circled areas below...
I also see yellow noise along with the magenta.
1) Possibly processing artifacts from in camera or in post. Are you shooting RAW or jpeg? Is it happening in the original image or in post processing?
2) Reflections from colored objects in the room or light coming though a window or relecting off glass and creating a prism effect.
3) Are you down converting your color bit depth or converting to a substandard profile?
4) Do you have the saturation cranked up? It looks oversaturated, especially on the skin. There is noticeable clipping.
5) Have you switched your lights to see if it's a failing bulb? It could be an old bulb.
6) Are you using a filter? It may be dirty or smeared.
My guess is saturation/clipping based on limited info and what I see in the pic.
First of all. Make some more tests.
Take a photo of a pure white surface, a piece of new paper, take it out of focus and take a look. Try to isolate some other factors, like the time you are using the camera (this can heat the sensor) or room temperature.
There is a chance something is happening to your sensor, probably some overheating.
(I have a similar problem with a video camera. I'll make some tests too)
(Offtopic. Probably you are pushing too much magenta into the processing, therefore exaggerating a bit a magenta cast)