I called Midiman and they said that the metallic hum was a sympton of a defective unit. They said they had some bad ones going around and that I should send it to them for a replacement. So it looks like I am sending it in. If anyone is interested, I'll let you know what they say.
Thanks for the responses.
It just sucks having to wait for this thing to come back. Guess I'll just have to route everything straight into the mixer and work on the midi side...