I only leave mine on at night if I 'm running a backup image or an in depth scan. CPU fan sounds like a Huey chopper.
Clean your fans....you would be amazed at the decible change.
I turn mine off every night. It's a me thing. Then there are the monthly cleanings, because it is so damn dusty here, even in the winter, and the occasional involutary hard shut downs when I am in the middle of something....usually due to some moron hitting a powerline, or Mother Nature playing havoc with us.