I too had this hum issue. I searched online for a while and came a cross a site detailing all the different ways to control a fan, but I can't find it in my history anymore. Basically there are 2 ways to control a fan without noise, one is an autotransformer or (variac) and the other is with a capacitor fan speed controller, like the ones that control a ceiling fan. I got this a Hunter 4 Speed Slide Fan Control and it works great with my Can Fan 6" RO at medium setting. It does take a little bit of work making a box that fits this and an outlet. But it's doable.