Unless something was wrong with the Hik's fans, it will be tough to find an NVR quieter than that.

Might I suggest working on the other end of the problem. Line the cabinet with an open cell acoustic foam. I like using this: [Link: amazon.com]
It does a very good job at absorbing mid to high frequency noises in a cabinet (like fan noise).
Cover all the wall surfaces (including the backside of the doors) and cut out the openings for your cabinet fans and air inlets.