I have a pair of Yamaha HS50M powered studio monitors that I plug into my MacBook Pro's audio port. Normally, there's no problem. However, when I plug in my D-Link 7 port powered USB hub, a high-pitched static sound comes from the speakers. It doesn't matter whether the hub is plugged into AC power or not. Any ideas for how to fix this? If need be, I'll buy another USB hub if there's something about this one specifically that's causing the issue. But eliminating a hub entirely isn't really an option. I need it there, but I need the audio as well. Any ideas?