I like my Tevo Flash but the noises of the main fan are too much.
You can find many creative approaches on the web, that's mine.
The first step towards noise reduction is to increase the air intake to 35-37mm.
The original cutout had a diameter of only 30mm and produced unnecessary wind noise.
Since the choice of quiet radial fans is very limited and a 50x15 fan is too unsafe for me for long term operation, I use two better 12V fans.
The 50x15 is with 25db quite quiet and inexpensive to get.
The 40x40x30 is a server fan and designed for 7x24h operation.
Even if the 50x15 should fail, the performance of the 40x40x30 is enough to protect the electronics.
So that the two 12V fans can operate safely with 24V, you only have to connect them in serial. This is the easiest way but depending on the fan quality not the quietest.
Another would be to use a suitable step-down circuit to reduce the 24V to 12V.
!!!!!! In this case the fans have to be connected in parallel. !!!!!!!!
Another advantage here is the possibility to change the speed with the potentiometer.
In my case, I reduced the voltage to 7.5 volts and achieved a very good ratio between cooling power and noise.
Try it ;-)