I use mine with a laptop so I don't have anything plugged into the USB power port. However, I have plugged an iPod into the audio jack under battery power and didn't hear any artifacts. I suspect if you hear whining when plugged into the USB power port, then that implies the power port is not adequately filtered. It could be a design issue or "bad" parts.
With regard to the loudness, do you have an EP0 plugged in? I'm in a 1,000 cubic foot office and I find that they are plenty loud but I use a powered sub as well.
