Noise should be a main concern when shopping for a whole house fan, because the hours while you are sleeping offer the coolest temperatures of the day. More important than simply exchanging the air, the cooling of the thermal mass of the structure down to the core simply takes time. Unfortunately, you can not wring all of the heat out of the thermal mass like a sponge - it just takes time - and a bit of stady, constant airflow. In this way, Running a fan overnight while you are sleeping will take advantage of these cooler temperatures, making your fan more effective on more days of the year, and reducing your need for A/C to a minimum.
Some manufacturers have incorporated ECM (electronically commutated motor) technology into whole house fans. This not only delivers AMAZING efficiency numbers, but the brushless motor design also offers extremely low noise levels.
With older, brushed motors, turning them down to a lower speed using a rheostat can reduce the noise level slightly, but you will notice that the power consumption stays roughly the same. On the other hand, ECM technology allows you to not have to trade efficiency for noise level, and you can actually maximize efficiency while minimizing noise level.
Whole house fans + ECM motors = A perfect combination for quiet, effective, efficient natural cooling.
They may cost a bit more, but considering the outstanding efficiency numbers and low noise levels, a modern whole house fan (especially those using an ECM motor) is definitely a worthwhile investment.
Cheaper whole house fans are too noisy that they in many cases go unused, or they are turned off too early in the evening, before it has really cooled off outside.