If your able to run the fan off your MB rather than the PSU you should be able to reduce the RPM's and the noise. The MB should regulate the fan speed based on temps. At times it may not even spin.
For the CPU fan, check the bios and see if cool n quiet is enabled. If not you may want to enable that, but be aware that it will also manage your CPU's clock speed up and down based on the load.
Hope this helps