Red noise

Hi everyone! Im new in blender and trying to improve my skills so far. I faced with a problem that I cant handle with. When im changing in “Light paths” menu Limited global illumination to Full global illumination I have a lot of red noise on my pic. I changed diffuse value from 128 to smthing like 15 or even 5, it helped but I don’t sure if its correct for realistic pic. If any one knows what kid of problem is that pls help to fix it.