How much speaker hum is normal...if any?

[DeadDog]

I recently purchased a new receiver and speakers:

Sony STR-DG820
Energy RC-Mini Center
Energy RC-10 L/R Fronts

Everything is hooked up correctly and sounds really good. I previously had a HTiB system and never really listened too closely to the ambient noises it would make. Now that I have this I want to make sure everything is crystal clear . When I place my ear next to/real close to the the speakers (including the old HTiB speakers in the back) there is a slight hum. It's mostly noticeable from the twitters (more prominent) but also comes from the woofers as well. My question is, how normal is this?

I know I had a ground issue with my tv cable but have since fixed that. I tried to unplug everything, except the receiver, to try and isolate what may be causing it. Even with everything unplugged (including the tv cable) it is still there. It's not noticeable during normal playing, only really when I have the receiver muted and get close to the speakers to listen for it.

Any help as always is appreciated. Thanks in advance.