I've tried the 9v/3a and the iFi vs the stock but only very briefly. I may this weekend when I get more time. The only thing I *thought* I heard was there was more body to the sound signature with the 3A and iFi 2A vs the stock. But don't quote me on that yet. At home I have the iFi plugged into a Furman power conditioner with an iFi AC iPurifier in that same wall outlet. No hum. I also have it plugged in at work right now into a regular cheapo power strip and there's no hum. Can you describe more about the hum you're hearing?