We tested our Roku 4 for over 3 hours of constant use and had no issues with fan noise. The Roku 4 fan should not be a issue and if you are hearing a lot of fan noise you need to do two things.
First make sure you are not blocking the two vents on the bottom of the Roku 4.
Second make sure you do not put it in a small cabinet that also has a lot of other devices making heat.
If you still have a loud fan noise you need to call Roku to return it.