Fan noise T36xx, T56xx, T76xx

Hi all, 

I bought myself a used T3600 system and would like to ask owners for advice on how make it quieter.

I am not planning to stress the PC, will only use it for light tasks. 

My current strategy is the following: 

Graphics:

Replaced the Quadro 4000 with a new and silent GeForce 

CPU:

The CPU fan is relatively quiet (~800rpm) but the temp is in the 60C+ range.

I might exchange the fan for a Noctua one to bring the temperature down.

-> Has anyone done that? 

System fans:

They are currently running at (~800rpm) with some minor noises.

I will use Speedfan to bring them down to a quieter level at ~600rpm. 

PSU:

That’s the one that bothers me the most.

The fans spin continuously (unknown speed) with a slightly annoying, but not air plane type, noise.

-> Are your PSU fans also running all the time?

-> Is there a way to reduce the speed of the fans via software? 

-> Any other suggestions to bring the noise level down? 

Help is very much appreciated