Cool your room down. Although you don't want to add more fans, consider replacing an 80mm with a 120mm on a side panel if you can. It moves more air and it's quieter. You could also switch an 80mm with an 80mm Vantec Tornado fan, but the noise is unbelievable!
I use mostly Koolance water cases, but have two computers in Antec Super Lanboy cases ($69) that have 120mm fans in the front and back, and the HSF I changed to the $15 Aero 7 Lite. These actually run cooler and quieter than the Koolance cases.