Yes. See also my previous post 
My HiFive Unmatched is using the 40mm to 25mm fan adapter with a 40mm Noctua and 120mm chassis intake fan. It’s sitting silently at 36.8°C MB/46°C CPU after 4 days of package(s) compilation at 25°C room temperature and 60% humidity.
The 40mm Noctua fan alone does not have enough CFM to cool the CPU efficiently. A4x20 FLX is a 5.5 CFM fan, but since the surface area is larger, the airflow output is lower as a result. In this setup, an intake case fan is required to compensate the airflow.
It’s much easier to find a silent 120mm chassis fan, so in the end it should still result in a much more silent setup.