He has been at war with his brother Rachlav since before 1100. There was some sordid little humiliation at the heart of it, something about a mortal favored by them both, and quite a bit of bloodshed and mutual provocation since. They detest each other thoroughly (but apparently they detest the Tremere even more).
Noriz himself found their little quarrel amusing, and had no intention of doing anything to halt it. Noriz favored bloodshed as an entertainment, so long as the blood being spilt was not his own.
Dark Ages Clan Novel: Tzimisce, p. 77, etc.