Hi @NIKOS-TSIDILAS, welcome to the community.
If you shoot 3200 ISO you are very likely to see noise in the shadow areas. This is normal, especially if you are under-exposing. Try shooting at lower ISO, light your subject better, or look for processing solutions that will reduce noise.
At higher ISO, you will generally see less noise if you over-expose slightly, but it's difficult to give any specific advice without seeng the problem first-hand. Uploading or linking to examples of the problem would help!
Best wishes
Mick
