According my experience, noise is the combination of four factors:
1- Sensor technology
2- Image processor
3- Underexposure
4- RAW processing software used
Points 3 and 4 being are the most sensitive in terms of responsibilities.
What RAW processing software do you work with?
X-T2 samples @ 800 ISO
https://flic.kr/p/2hup5HK
https://flic.kr/p/2frdEEr
Samples @ 1600 ISO
https://flic.kr/p/2gaWZTm
https://flic.kr/p/2goSUi7