The fans are a problem, and especially in the summer, when the whole house is warmer... (Is that the edge of technology ?).
When I really can't take it anymore, I keep the Energy Saver window (in System Preferences) open in the back, and switch back to Reduced when I want quietness and don't need to edit photos or movies.
I usually get a quick change of noise. But it sucks to have to slow down your computer for quietness.
I also guess that if the computer is too warm, it will still need some time with the fans, even in Reduced, to get back to a cooler temp.
Do you have enough room for cooling air ? The space under the iMac should be left empty, as well as the space behind the iMac. If you just circulate warm air, it won't cool down. Don't keep your iMac stuck to a wall (or a chimney...).