The humming sound is actually caused by our dirty power line aka A/C line noise. It's normal to hear humming sound from transformers of your Hi-Fi stuff. That's why you need a power conditioner, something like the one below or any other brands you can find in the market.



PS Audio UPC-200HB

I'm not sure about the latest price but it aint't cheap b'coz it's an audiophile product, it could even enhance the picture quality from your LCD if connected to it. I didn't buy it as I have other plans in mind, planning to buy Wireworld power cord and Tundra (power strip), another alternative method to surpress A/C line noise effectively.

Can you try taking the speakers to your friend's place to test it, just wanna see if it's due to A/C line noise or you might have a faulty transformer.