floriske wrote:The fans are VERY loud though, so I am going to remove them and add 120mm fans for cooling.
It depends on the power supply but you probably wont be able to do this. The circuitry will likely include monitoring of the fan i.e. if the fan stops the power supply immediately shuts down. You could test for this by inserting a plastic cable tie or similar through the vents to prevent the fan blades from turning, then switch on the power supply and if it quickly shuts down then it is monitored.
The faster the fan runs the more noise it makes and if it runs at a constant speed, as it probably does, then it supplies enough cooling for when the power supply is providing maximum current. If you're not going to use the maximum output then you could add an inline 5V regulator to drop the 12V fan supply to 5V. All being well this will be enough for the monitoring not to cut in.
I have purchased an inexpensive power supply from a Dell server and this will supply 12V at 175A. It has 1 x 92mm fan and 2 x 60mm fans, all of which are very noisy so I need to do something similar. The four motors will draw a maximum of 120A and then only when they're all running at maximum, so I will be drawing quite a bit less than the maximum 175A.