Well, my build's case fan is intolerably loud. I am going to buy a new one tomorrow, but the rig needs to run all night to finish a download - would it be acceptable to run the rig only for that time without the case fan?
Taking off the side panels will assist in keeping it cool, if temps start rising up, put a small fan (box fan?) near the pc, it will help. I have done it a few times in a pinch. Not recommended for long term...as dust will become a problem.
Just take off the side panels, and take off the fans. Why do you need it to download overnight? Is it some top secret G45 government file that if you do not receive you will be assassinated? An open test bench runs with no fans by the way... but it's not concealed within a case. Just expect slightly hotter/cooler temps.