Is your PSU looks new or used, could be just dirty inside. Since it is proprietary form factor, you don't have much choice. So, if it would be me, I would open PSU box without pulling any cables, just a cover, if possible and look at fan, it could be defective - something bent or touching, not sure. If you get to the point changing PSU fan, you would not stop it from working all the time, but you might be able to eliminate the excessive noise.
For CPU. Do you have any monitoring software to see your fan speeds and temperatures?
May be you did not applied thermal paste well, or used low grade thermal paste and your CPU just runs hot?
What was your CPU upgrade, original one and final one?
Have you changed heatsink to copper (or do you have copper)?
Please answer those questions, all of them.