I have a Dahua NVR but I'm sure this would work with anything.
Noctua 5v fan (runs at about 15db at 100%)
Noctua A-Series Cooling Fan Blades with AAO Frame, SSO2 Bearing (NF-A4X10-FLX 5V)
https://www.amazon.com/gp/product/B00NEMGCIA/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
3-pin reducer...