Because the original fan of the Elegoo Mars 3 runs all the time, is way too loud and absolutely annoying, I swapped it for a 40x40x20mm Noctua fan.

To improve the cooling with this smaller fan, I also constructed an air duct to draw the warm air out of the case instead of just mixing it around inside the housing as Elegoo originally did.

In addition, I changed the LED fan output in the configuration from "always on" to "only when printing" and used a second Noctua fan of 40x40x10mm for permanent cooling of the board at reduced speed.

Since the fan outputs on the Mars 3 board are 24V, I use cheap adjusable step down converters from Aliexpress (the two circuits in heat shrink tube in the foreground) to allow using 12V fans and adjusting the fan speeds. But of course you can also use resistors to get the appropriate voltages and speeds.

All parts are printed from TPU to reduce vibration. No supports needed.
I also put sound-absorbing adhesive tape around the lamp funnel.

In the photos, one of my pieces is printed in black, not transparent like the others this is only because it fit well enough in my test print from PET, so I didn't print it again in TPU. 

The two spacers are used to utilize the original fastening screws to assemble the construction. They don't need to be used, but depending on the heads of your screws it can get a little tight with the fan.

Two more short screws are required to fasten the first air duct. The second air duct is plugged to the first on one side and can be glued or stuck with double sided adhesive tape on the other side.

I simply stuck the second fan bracket to the metal plate with double sided adhesive tape so that the fan is cooling the board and stepper motor.

Printer is running fine, much quieter and the exhaust air is not even warm.
So I reduced the fan speeds further.