Okay gang, need some input. Jusy bought an ipower 6" exhaust fan to replace my 4" fan. When I use my Active Air speed controller, there is a very noticeable hum that can be heard in adjacent rooms. And this is after I enclosed the fan and packed with insulation. I have read online that cheap speed controllers can cause fans to have a noticeable hum because they are basically cycling electrical current on and off to adjust speed. The answer appears to be that a variac transformer will eliminate hum and be safer to operate. Before I spend another $50, can anyone varify this is how I need to go to reduce/elimanate fan hum?