@Swedishkiller12 Undervolting a 12V fan on the Pis 5V or even 3.3V pin is not going to give you any benefit. In fact it most likely is going to move a lower volume of air then your 5V fan on the 3.3V rail.

Fan noise really comes down to two things. Air turbulence (fan speed/fin design) and ball bearing quality/noise.

Spinning your fan slower and having an adequate passive cooler on the SOC is likely your best bet.

Have you measured/logged temperatures while under load? If you can do this while running on the 3.3V pin and are staying below the ideal max of 70C (this is not the absolute max, but rather the safe longterm max for most models) then you should be fine.

@mitu it came back :/

My pi3 b+ came in today. The flirc cases fits fine. I'm using a thermal pad I had lying around from a pc gpu.

In my arcade build i found the fan that came with the flat pack kit was really loud when run from full power. It was a 12v fan. So i just found a left over 5v power brick and connected that to the fan and it runs about half speed, just the perfect amount of air flow without the noise.